OBD-II Code U1346: Engine Control Module LIN Bus 2 Communication Failure

What Does U1346 Mean?

U1346 means the Engine Control Module (ECM) lost communication with a sensor on LIN bus 2. On affected GM vehicles, this specific network is dedicated to the Mass Airflow (MAF) sensor. The ECM expects a constant data stream; when the signal drops for more than 3 seconds, it triggers this code.

Technical definition: U1346 is officially defined as 'Engine Control Module LIN Bus 2'. It indicates a communication failure on a single-wire Local Interconnect Network (LIN) where the ECM is the master. The ECM detected a loss of communication with a slave device (almost always the MAF sensor on GM vehicles) for 3 seconds or more.

Can I Drive With U1346?

⚠️Yes, But With Caution. You can drive, but immediate attention is required. On GM vehicles, this code triggers 'Reduced Engine Power' mode, causing a sudden, dangerous loss of speed (e.g., 70mph to 35mph in seconds). Continued driving causes stalling, unpredictable shifting, or a no-start condition. The safety risks of sudden power loss on a highway are significant.

Common Causes

• Chafed or Broken Wiring Harness (Very Common) — This is the most frequent cause on newer GM vehicles. The factory wiring harness to the Mass Airflow (MAF) sensor is too short or secured with an overly tight zip tie. Engine movement causes the LIN bus wire to chafe and break internally near the connector.
• Loose or Corroded Connector Pins (Common) — Moisture intrusion causes pins inside the MAF sensor connector to loosen or corrode. This creates high resistance and interrupts the LIN bus communication signal.
• Improper Maintenance or Aftermarket Intake Installation (Common) — Installing a cold air intake or moving the airbox during a filter change puts extra stress on the tight MAF sensor wiring harness. This stretches the harness and snaps already-weakened internal wires.
• Faulty Mass Airflow (MAF) Sensor (Less Common) — The MAF sensor's internal circuit board or LIN transceiver chip fails, stopping communication with the ECM. This is significantly less common than a wiring issue; always test the harness first.
• Engine Control Module (ECM) Software Glitch (Uncommon) — A bug in the ECM software falsely flags a communication error. GM TSB PIP5934 addresses this on specific trucks, requiring a dealer software update rather than physical repairs.
• Loose or Corroded Ground Connection (Uncommon) — A poor ground connection for the ECM or sensor circuit introduces electrical noise, disrupting the low-voltage LIN bus signal.
• Blown Fuse (Rare) — A short circuit blows the fuse powering the sensor or communication line, instantly cutting off the LIN bus signal.

Symptoms

• Check Engine Light is On — The Malfunction Indicator Lamp (MIL) illuminates immediately when the ECM detects the communication loss.
• Reduced Engine Power Message — The vehicle displays a 'Reduced Engine Power' warning and severely limits acceleration to prevent engine damage.
• Engine Hesitation or Stumbling — As the wiring fails intermittently, the engine hesitates, stumbles, or runs rough during acceleration due to erratic airflow data.
• Rough or Harsh Transmission Shifting — Without accurate MAF sensor data, the ECM cannot calculate engine load, forcing the transmission to command harsh, poorly timed shifts.
• Engine Won't Start — In severe cases on highly integrated vehicles (like the C8 Corvette), this communication failure prevents the engine from starting entirely.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this code.

Common Fixes & Costs

• Repairing the MAF Sensor Wiring Harness — Parts: $5-$20, Labor: $250-$600, ~2.5 hr book time (Professional)
• Replacing the MAF Sensor Connector Pigtail — Parts: $40-$90, Labor: $150-$250, ~1.5 hr book time (Intermediate)
  Buick Encore GX / Chevrolet Trailblazer (1.2L/1.3L): OEM GM Connector Kit: 85519071 or 85518225 (Alt: Various unbranded pigtails available.)
  Chevrolet Silverado / GMC Sierra: OEM GM Genuine Parts: PT2782 (Alt: Standard Motor Products: S2507, Duralast: CONB11450)
• Updating/Reprogramming the Engine Control Module (ECM) — Parts: $0, Labor: $100-$250, ~1.0 hr book time (Professional)
• Replacing the Mass Airflow (MAF) Sensor — Parts: $100-$350, Labor: $50-$100, ~0.5 hr book time (DIY)
  Chevrolet Silverado / GMC Sierra (5.3L L84 V8): OEM ACDelco: AF10530 (Alt: Bosch: 0280218419, Denso: 221-9501)
  Chevrolet Silverado / GMC Sierra (2.7L L3B I4): OEM ACDelco: AF10531 (Alt: Standard Motor Products: MAS0438)
• Securing or Repairing a Ground Connection — Parts: $1-$10, Labor: $75-$150, ~0.8 hr book time (Intermediate)

Used vs. New Parts: Buying Guide

When a used part is worth it: Never buy used wiring pigtails. A used MAF sensor from a low-mileage donor is a budget option, but the minimal savings rarely justify the risk of inheriting another failing electronic component.

Donor-vehicle mileage cap: roughly under 30000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Verify donor vehicle was not scrapped for engine or electrical issues.
• Match the part number exactly; visual similarities are not enough.
• Avoid sensors from vehicles with high mileage or unknown history.

Decision logic:

• If The part is a wiring pigtail or connector → Always buy new. Used wiring is not a reliable repair.
• If The part is a MAF sensor and the vehicle is under 100K miles → Buy a new OEM or high-quality aftermarket sensor. The price difference doesn't justify the risk of a used part failing soon.
• If The budget is extremely tight and the fault has been confirmed to be the sensor itself → A used sensor is a gamble but works temporarily. Expect a much shorter lifespan.

Warranty tradeoff: Used parts typically have a 30-90 day warranty at best. New aftermarket sensors often carry a 1-year to limited lifetime warranty. New OEM parts carry a manufacturer's warranty (typically 12 months).

Worst-case if a used part fails: $150-$400 if a used MAF sensor is bad or fails shortly after installation, requiring repeat labor costs plus the cost of another part.

What Happens If You Wait — Timeline

1. 0-1 week: Code U1346 sets, Check Engine Light illuminates, and 'Reduced Engine Power' mode activates. Drivability is severely limited, capping speed at ~35 mph. (MPG impact: 10-20%% · Added cost: $0)
2. 1 week - 2 months: The engine runs exclusively on default, rich fuel maps because it lacks airflow data. This slashes fuel economy and fouls spark plugs. (MPG impact: 15-25%% · Added cost: $50-$200 in wasted fuel and potential spark plug replacement.)
3. 2-6 months: Sustained operation with a rich fuel mixture overheats the catalytic converter as it burns off excess fuel, cracking or melting the internal ceramic substrate. (MPG impact: 15-25%% · Added cost: $1500-$3500 (catalytic converter replacement is now required).)
4. 6+ months: Complete catalytic converter meltdown causes a major exhaust blockage. The engine loses all power, fails to start, and suffers internal damage from excessive backpressure. (MPG impact: 25-50%% · Added cost: $1500-$3500+)

Cost of Not Fixing It

• 0-1 month: Annoying 'Reduced Engine Power' mode and a 10-20% drop in fuel economy as the engine runs on default (rich) fuel maps. Risk of stalling or hesitation in traffic. (Added cost: $50-$150 in wasted fuel)
• 1-6 months: Continued driving on a rich fuel mixture overheats and damages the catalytic converter, leading to a much more expensive repair. It also fouls spark plugs and oxygen sensors. (Added cost: $1500-$3200 for catalytic converter replacement.)
• 6+ months: Catastrophic failure of the catalytic converter is highly probable. The vehicle will have extremely poor performance, fail any emissions test, and suffer long-term internal engine damage. (Added cost: $1500-$3500+)

Diagnosis Steps

1. Check for Technical Service Bulletins (TSBs)
   Search for TSBs related to your vehicle's year, make, model, and 'U1346'. GM bulletins #22-NA-008 and PIP5934 pinpoint the exact cause and advise against replacing parts as a first step.
   Tools: Internet access (Beginner)
2. Perform a 'Wiggle Test'
   With the engine running, vigorously wiggle the MAF sensor wiring harness near the connector and retainer clips. If the engine stumbles, stalls, or the check engine light flickers, you have confirmed an internal wire break.
   Tools: None (Beginner)
3. Perform a Visual Inspection
   Locate the MAF sensor on the air intake tube. Ensure the electrical connector is fully seated. Inspect the wiring harness for chafing or tight zip ties, paying close attention to the harness retainer clips.
   Tools: Flashlight (Beginner)
4. Pro Tip: Analyze Scan Tool Live Data (PIDs)
   Using a scan tool, monitor the Mass Air Flow Rate PID. A healthy 5.3L engine reads 5-6 g/s at idle. If the PID reads 0 g/s or freezes, it confirms a total loss of communication.
   Tools: Professional OBD-II Scan Tool with Live Data (Advanced)
5. Clear the Code and Test Drive
   Use an OBD-II scanner to clear the code. Drive the vehicle to see if the code returns immediately. If it returns, a hard fault exists in the wiring or sensor.
   Tools: OBD-II Scanner (Beginner)
6. Pro Tip: Test LIN Bus Voltage with a Multimeter
   Set a digital multimeter to DC volts and 'Peak Min/Max'. Back-probe the LIN bus signal wire at the MAF connector with the engine running. A healthy bus fluctuates between ~1V and ~12V. A steady 12V indicates an open wire or faulty sensor.
   Tools: Digital Multimeter with Min/Max, vehicle-specific wiring diagram, back-probe pins (Advanced)
7. Inspect Fuses
   Locate the fuse boxes and identify fuses related to the ECM or engine sensors. Visually inspect them for a broken filament.
   Tools: Owner's manual, fuse puller or needle-nose pliers (Intermediate)
8. Pro Tip: Analyze the LIN Bus with an Oscilloscope
   Connect a lab scope to the LIN bus signal wire. A healthy bus shows square-wave data packets (1V to 12V). Unplug the MAF sensor; if the signal flatlines at 12V, the wiring to the ECM is intact, pointing to a bad sensor.
   Tools: Automotive oscilloscope, wiring diagram, back-probe pins (Advanced)
9. Isolate the Fault
   If the wiggle test fails but voltage tests show a fault, check for continuity on the power, ground, and signal wires between the MAF sensor and ECM to locate the exact break.
   Tools: Multimeter, wire stripping/cutting tools (Professional)

When This Code Triggers (Freeze-Frame Conditions)

• Engine Coolant Temp: 180-200°F (82-93°C) (The code sets when the engine is fully warmed up and has been running for several minutes.)
• RPM: 1500-2500 RPM (The fault is frequently triggered under steady-state cruising conditions, not typically during hard acceleration or at idle.)
• Engine Load: 20-50% (Light to moderate engine load, consistent with highway cruising or maintaining speed on a level road.)
• Vehicle Speed: 45-65 mph (72-105 km/h) (The loss of communication is detected during constant highway driving when the ECM expects a stable signal from the MAF sensor.)

Related Codes

• U060F — Means 'Lost Communication With Mass Air Flow Sensor' and is almost always present with U1346. U1346 is the general alarm, while U060F specifies the MAF sensor is the unresponsive device.
• P0101 — Indicates the MAF sensor is sending illogical data. It often appears as a precursor to U1346, as a failing wire sends erratic signals before the connection is lost completely.
• P0102 — Means 'Mass Air Flow Circuit Low'. This is caused by a failing wire shorting to ground just before it breaks, leading to the total communication loss of U1346.
• U1345 / U1347 — Indicate failures on LIN Bus 1 and LIN Bus 3. Seeing these alongside U1346 suggests a wider problem, such as a faulty ECM or a major power/ground issue affecting multiple buses.

Climate & Environmental Factors

• Cold Weather: Wire insulation becomes hard and brittle in low temperatures. Engine movement snaps already-strained and brittle wires, contributing to the high failure rate of tight MAF harnesses in colder climates.

How to Talk to a Mechanic About This Code

Say this: "I have a Check Engine Light on my [Vehicle Year/Make/Model] with codes U1346 and U060F. I know this is a common MAF sensor wiring harness issue on these models. I need a diagnostic appointment to perform a wiggle test and confirm a wiring fault before replacing any parts."

This signals you are an informed customer. It immediately directs the technician to the most likely cause (wiring) and away from the less likely, more expensive first step of replacing the MAF sensor. Mentioning the TSBs (#22-NA-008 or PIP5934) if applicable is even better.

Avoid saying:

• 'My check engine light is on, can you look at it?'
• 'My truck is in limp mode.'
• 'Just replace the MAF sensor.'

Questions to ask before authorizing the repair:

• Did you perform a 'wiggle test' on the MAF sensor harness? What was the result?
• Did you find a broken wire, or are you recommending a new MAF sensor? If it's the sensor, how did you rule out a wiring break?
• Is this repair covered by GM's Bumper-to-Bumper or Powertrain warranty, or any Technical Service Bulletins?
• If you are repairing the wire, will you be adding slack to the harness to prevent this from happening again?
• What is the warranty on this specific repair?

Where to Take It: Dealer vs Independent vs Chain

• Dealer: Best fit for in-warranty vehicles. They have direct access to all TSBs and perform the repair for free if covered.
  Best for: Vehicles still under the Bumper-to-Bumper (3yr/36k) or Powertrain (5yr/60k) warranty., Cases where a software update (reprogramming) is required per a TSB., Confirming warranty coverage for a known issue like TSB #22-NA-008.
  Downsides: Highest labor rates., May be quick to replace a pigtail or sensor when a simpler wire repair would suffice (if not under warranty). (Typical cost: +50% vs. baseline)
• Independent Shop: Excellent fit for out-of-warranty repairs, provided you choose a reputable shop. A good independent technician performs the common wiring harness repair for significantly less than a dealer.
  Best for: Out-of-warranty vehicles where cost is a primary concern., Shops with good reviews for electrical and diagnostic work.
  Downsides: Quality and diagnostic skill vary widely., May not have access to the latest TSBs if they don't subscribe to professional data services. (Typical cost: +0% vs. baseline)
• Chain Shop: AVOID for diagnosis. Technicians will likely use a parts-cannon approach, replacing the expensive MAF sensor without checking the known wiring fault.
  Best for: Simple part replacement IF you have already 100% diagnosed the fault yourself.
  Downsides: High risk of misdiagnosis., Technicians are more likely to replace the MAF sensor without testing the wiring, leading to wasted money when the code returns. (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the estimated repair cost exceeds 40-50% of the car's private-party value, you should pause and evaluate your options.

• Car worth $25000, fix is $600: Fix it. The repair cost is less than 3% of the vehicle's value, which is a minor expense for a critical drivability issue.
• Car worth $15000, fix is $600: Fix it. The repair cost is only 4% of the vehicle's value. This is a routine repair cost for a modern vehicle.
• Car worth $4000, fix is $600: Borderline, but worth fixing. The cost is 15% of the car's value. Since the issue prevents normal driving, the car's 'as-is' value is severely diminished. Fixing it restores full utility.

What Scan Tool You Need for This Code

Minimum: A basic OBD-II code reader that can read and clear codes. This is enough to confirm U1346 and U060F are present.

A basic reader cannot view live data. Proper diagnosis requires monitoring the Mass Air Flow (g/s) PID to confirm it reads 0 or freezes, proving a communication loss rather than a dirty sensor.

Budget: BlueDriver Pro (~$100) — Connects to your phone via Bluetooth. It reads codes, provides freeze-frame data, and graphs live data so you can monitor the MAF sensor's g/s reading in real-time.

Mid-range: Foxwell NT510 Elite (with GM Software) (~$200) — A powerful handheld unit providing OE-level diagnostics for GM vehicles. It offers fast live data graphing for the MAF sensor and accesses manufacturer-specific codes beyond the basics.

Professional: Autel MaxiCOM MK808 / MK808BT (~$450-600) — A professional-level tablet scanner offering comprehensive diagnostics, fast live data, and bidirectional controls. Its main advantage is speed and access to all vehicle modules.

Rent vs buy: For a one-time code read, use AutoZone's free Loan-A-Tool program to borrow a basic scanner. However, since the key diagnostic step for a DIYer is watching live data, buying a budget pick like the BlueDriver is a smart investment.

How to Clear the Code After You Fix It

1. Use an OBD-II scan tool to clear the code
2. Perform the GM General Drive Cycle to reset readiness monitors
3. Do not disconnect the battery, as this clears monitors and may not clear the code permanently

Drive cycle (~20 minutes): Cold start (coolant temp below 122°F). Idle for 2-3 minutes with electrical loads (A/C, defroster) on. Accelerate to 55 mph and hold steady for 3 minutes. Let vehicle coast down to 20 mph without braking. Accelerate to 55-60 mph and hold steady for 5 minutes. Coast down to 0 mph.

Readiness monitors affected: Catalyst Monitor, Evaporative System Monitor, Oxygen Sensor Monitor

Before emissions retest: drive at least 50 miles to fully set monitors.

Watch out for:

• Clearing the code without performing a drive cycle results in failing an emissions test because readiness monitors are 'Not Ready'.
• If the underlying wiring issue is not fixed, the code returns almost immediately upon starting the vehicle or during the test drive.

Will This Fail Emissions / State Inspection?

Yes — this code typically fails an OBD-II emissions inspection.

• California: An illuminated Check Engine Light is an automatic failure. After repair, a complete drive cycle must be performed to set all readiness monitors to 'Ready' before a retest can pass.
• New York: A vehicle with an illuminated Check Engine Light automatically fails the emissions inspection. If codes are cleared, the vehicle cannot be tested until the required readiness monitors are set.
• Texas: In the 17 counties requiring emissions testing, an active U1346 code and illuminated Check Engine Light causes an automatic failure of the OBD-II test.

Most Commonly Affected Vehicles

• Chevrolet Silverado 1500 (2019-2024) — Extremely common due to a short MAF sensor wiring harness. TSB PIP5934 addresses 2022-2023 models with the 2.7L engine, but the 5.3L V8 is also widely affected.
• GMC Sierra 1500 (2019-2024) — Mechanically identical to the Silverado, it suffers from the exact same wiring harness design flaw.
• Buick Encore GX (2020-2023) — Specifically named in GM TSB #22-NA-008 for a wire breaking near a zip tie on the MAF sensor harness due to excessive tension.
• Chevrolet Trailblazer (2021-2023) — Named in GM TSB #22-NA-008 for the same wiring harness issue as the Buick Encore GX.
• Cadillac XT4 (2019-2023) — Built on a similar platform and sharing powertrain components with other affected GM SUVs, experiencing identical MAF sensor wiring harness failures.
• GMC Yukon / Yukon XL (2021-2024) — Shares its platform and V8 engine options with the Silverado/Sierra, making it susceptible to the same MAF wiring harness chafing.
• Chevrolet Tahoe / Suburban (2021-2024) — As the Chevrolet counterpart to the Yukon, these are equally affected by the MAF sensor wiring harness design flaw.
• Chevrolet Corvette (C8) (2020-2024) — This code causes a severe communication failure resulting in a no-start condition on the C8 platform.

Manufacturer-Specific Notes

• General Motors (Chevrolet, GMC, Buick, Cadillac): GM has a widespread issue where the MAF sensor wiring harness is too short or secured by an overly tight zip tie, causing the LIN bus wire to break. TSB #22-NA-008 addresses this on SUVs, while PIP5934 addresses a software issue on trucks.
• General Motors (Warranty/Recall Information): There are no active safety recalls, but the repair is covered by GM's Bumper-to-Bumper Limited Warranty (3 years/36,000 miles) and often the Powertrain Limited Warranty (5 years/60,000 miles). TSB #22-NA-008 provides specific labor operations for warranty claims.
• Ford: Ford uses different code structures for LIN bus failures, often within the 'U0xxx' range. A similar failure on a Ford sets a code like U0104 or U0256, as LIN is used for different components.
• Chrysler / Jeep / Dodge: These brands do not typically use U1346. A LIN bus fault sets a brand-specific code or a generic 'U' code pointing to a specific module, such as the intelligent battery sensor (IBS).
• Jaguar / Land Rover: On JLR vehicles, U1346 is defined as 'Vehicle Speed Data Mismatch'. This is related to conflicting vehicle speed signals between modules and has nothing to do with a LIN bus or the MAF sensor.

Real Owner Stories

2019 Chevy Silverado 1500 5.3L at 98K miles

Check Engine Light and 'Reduced Engine Power' message appeared. Truck hesitated and ran rough.

What they tried:

1. Owner suspected a wiring issue based on forum research.

Outcome: An independent shop confirmed a chafed wiring harness. The repair took two days and cost $600. The shop noted that GM made the harness too short, causing it to rub and break as the engine moves.

Lesson: On modern GM trucks, a U1346 code is very likely a wiring harness issue, not a bad sensor. A 'wiggle test' confirms this before spending money on parts.

2020 Chevy Silverado 1500 2.7L at 40K miles

Code U1346 appeared immediately after the owner cleaned a K&N air filter and briefly ran the engine with the airbox detached.

What they tried:

1. Took the truck to an AutoZone for a code scan.
2. Received advice to clean the MAF sensor and use a gas treatment.

Outcome: Forum users correctly identified that cleaning would not fix an electrical communication code and that the issue was a temporary glitch from running with the sensor unplugged. The owner cleared the code and it did not return.

Lesson: Do not run the engine with the MAF sensor disconnected, as this sets communication codes. If the code appears after maintenance, first clear it with a scanner to see if it was a temporary fault.

2021 Chevy Trailblazer

Vehicle displayed 'Reduced Engine Power' message and set codes U1346 and U060F.

What they tried:

1. Owner took the vehicle to a GM dealer for diagnosis.

Outcome: The dealer diagnosed a broken wire at the MAF sensor connector pigtail, a known issue covered by TSB #22-NA-008. The repair involved replacing the connector pigtail. The repair was covered under the vehicle's warranty.

Lesson: This is a known manufacturing defect on certain GM models. Always check for TSBs related to your vehicle, as the repair is often covered under warranty.

2023 Buick Encore GX

Check Engine Light on with codes U1346 and U060F.

What they tried:

1. A technician performed a visual inspection and found no obvious damage.
2. The technician consulted GM TSB #22-NA-008, which described a wire breaking at a tight zip tie.

Outcome: Performing a 'wiggle test' on the harness near the specified zip tie caused the fault to appear and disappear, confirming the internal break. The wire was repaired according to the TSB, resolving the issue.

Lesson: Even without visible damage, an internal wire break is the most common cause. Following the diagnostic steps in official TSBs, like the 'wiggle test', is the fastest way to confirm the exact failure point.

How to Prevent This Code From Triggering

• Proactively Inspect and Add Slack to the MAF Harness (Once, or during any air filter change.) — Locate the MAF harness and identify the tight factory zip tie. Carefully cut it and replace it with a looser tie, or re-route the harness to provide slack, preventing the wire from snapping under engine torque.
• Wrap Harness in Protective Loom or Tape (Once, during inspection.) — Adding a layer of high-temperature cloth harness tape or split-loom tubing provides an extra barrier against abrasion and chafing. This protects the insulation from being rubbed through by engine components or clips.
• Apply Dielectric Grease to the Connector (During any maintenance where the MAF is disconnected.) — Applying a small amount of dielectric grease to the connector's seal blocks moisture and prevents corrosion on the pins, which causes communication faults.
• Exercise Caution During Air Filter Changes (Every air filter service.) — The wiring is fragile. Avoid pulling or putting tension on the MAF sensor harness when removing the airbox lid or intake tube. Forgetting to plug the sensor back in before starting the engine sets this code.

Frequently Asked Questions

Can I fix U1346 myself?

Yes, if it's a simple loose connector. However, the most common cause is a broken wire inside a harness, requiring diagnostic skill to locate and soldering experience to repair. Replacing the MAF sensor is easy but often wastes money since wiring is the true root cause.

Will cleaning my MAF sensor fix a U1346 code?

No. U1346 is an electrical communication failure code, not a performance code caused by a dirty sensor. Cleaning the sensing element will not repair a broken wire or a failed internal electronic component.

Why did my truck suddenly slow down on the highway?

This is the 'Reduced Engine Power' safety mode. When the ECM loses the critical airflow signal from the MAF sensor, it defaults to a safe, low-power mode to prevent engine damage. This feels like a sudden and alarming loss of speed.

I got this code after installing an aftermarket air intake. Did the intake cause it?

It likely triggered the failure. The factory wiring harness is often very tight, and moving it to fit an aftermarket intake breaks an already-strained wire. The root cause is fragile factory wiring, but the installation exposed the weakness.

Is this repair covered under my GM warranty?

Yes, if your vehicle is within the bumper-to-bumper (3yr/36k) or powertrain (5yr/60k) warranty periods. This is a known issue documented in multiple TSBs. Reinstall the factory air intake before your dealer visit to avoid warranty claim denial.

The mechanic wants to replace the MAF sensor right away. Is this correct?

Be cautious. A broken wire is far more common on these GM vehicles than a failed sensor. GM TSB PIP5934 specifically advises against replacing the MAF sensor for this code without thoroughly testing the wiring first.

What is the LIN bus voltage supposed to be?

A healthy GM LIN bus signal fluctuates rapidly. Measured with a multimeter on 'peak min/max', it shows a maximum near battery voltage (~12V) and a minimum around 1V. At rest, it shows a steady 12V.

Key Takeaways

• A broken wire in the Mass Airflow (MAF) sensor harness causes the vast majority of U1346 codes on 2019+ GM vehicles, usually due to an overly tight factory zip tie.
• This code triggers a dangerous 'Reduced Engine Power' mode that instantly limits acceleration and caps vehicle speed to around 35 mph.
• Perform a 'wiggle test' on the MAF sensor wiring harness with the engine running; if the engine stumbles, you have confirmed an internal wire break.
• Check GM Technical Service Bulletins (TSBs) #22-NA-008 and PIP5934 before buying parts, as they explicitly advise against replacing the MAF sensor for this code.