U1008 on 2018-2019 Alfa Romeo Stelvio: LIN 1 Bus Fault Causes and Fixes

What's Unique About the 2018-2019 Alfa Romeo STELVIO

The Alfa Romeo Giorgio platform, which underpins the Stelvio and Giulia, is known for having numerous software-related issues in its early model years. For the U1008 code specifically, Alfa Romeo has released multiple Technical Service Bulletins (TSBs) pointing to outdated PCM software as the root cause, rather than a physical part failure. These TSBs also note that the software update improves the strategy for the turbo coolant pump's operation to enhance the durability of turbo O-rings. This makes checking for software updates a critical first step, which is different from many other vehicles where a U-code might immediately suggest a wiring or component fault.

Diagnostic Flowchart

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

Symptoms You May Notice

• Malfunction Indicator Lamp (MIL) or Check Engine Light is on
• Failure to pass state emissions or vehicle certification inspections.
• Reduced engine performance or a feeling that the car is struggling to reach high speeds, even without a MIL.
• Potential for other warning lights related to specific systems on the LIN bus
• Reduced engine performance or drivability issues.
• Symptoms related to a failing Charge Air Cooler (CAC) coolant pump, such as reduced power under boost.
🎬 Watch: How to perform a charge air heater valve delete.
• Elevated intake air temperatures when monitored with a scan tool, which can be a precursor to damaging turbo O-rings.

Most Likely Causes

1. Outdated Powertrain Control Module (PCM) Software 🔴 High Probability → Shop Engine Control Module (ECM) Multiple TSBs were issued by Alfa Romeo to address this specific code and others by updating the PCM software on 2018-2019 models. These updates specifically revise the control strategy for components on the LIN 1 bus.
   How to confirm: A dealer or qualified shop must check the vehicle's current software version against the latest available updates referenced in TSBs like 18-045-23, 18-026-20, and 18-101-19.
   Typical fix: Reprogramming the PCM with the latest software using a wiTECH 2 scan tool. This often must be followed by a TCM software check and a 'Phonic Wheel Replacement' routine.
   Est. part cost: $0
2. Failing Auxiliary Water Pump Relay 🟡 Medium Probability → Shop Engine Water Pump The relay that controls the Charge Air Cooler (CAC) pump is a known failure point. It can fail intermittently, causing the U1008 code without illuminating the check engine light, leading to a noticeable loss of performance.
   How to confirm: A simple diagnostic test is to swap the CAC pump relay with an identical relay from a non-critical system (like the headlamp washers) and see if the code disappears and performance is restored. The relay is located in a fuse box behind the left-side headlamp. 🎬 Watch: How to fix a loss of power with a simple relay swap.
   Typical fix: Replace the faulty relay. Many owners choose to replace it as a preventative measure. The updated Mopar part is 06106094AA.
   Est. part cost: $20-$40
3. Failing Component on the LIN 1 Bus (CAC Pump) 🟡 Medium Probability A single faulty module can disrupt the entire network. The Charge Air Cooler (CAC) coolant pump is a known component on this bus that can fail. Its failure is often preceded by the failure of its control relay.
   How to confirm: If a software update and relay replacement don't fix the issue, a technician will use a scan tool to see which module is not responding. They may disconnect modules on the LIN 1 bus one-by-one to isolate the faulty component.
   Typical fix: Replace the specific sensor or module that has failed. This is often the Charge Air Cooler (CAC) coolant pump. 🎬 See this walkthrough on upgrading the electric water pump.
   Est. part cost: $150-$400
4. Wiring Harness or Connector Issue ⚪ Low Probability
   How to confirm: Visual inspection of the LIN 1 bus wiring for chafing, corrosion, or loose pins at module connectors. A multimeter would be used to check for continuity, shorts to ground, or shorts to power on the LIN circuit.
   Typical fix: Repairing the damaged section of the wiring harness or cleaning/replacing the affected connector.
   Est. part cost: $10-$100

Rare But Worth Checking

• Failing Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) While rare, the PCM itself can fail. This should only be considered after all other possibilities, including software, components, and wiring, have been exhaustively ruled out.
• Weak Battery or Poor Connection: The complex electronics on the Stelvio are highly sensitive to battery voltage. A weak or dying battery, or corroded terminals, can cause a cascade of seemingly unrelated communication errors, including U1008. Always ensure the battery is fully charged and the terminals are clean before diagnosing network faults.

Diagnosis Steps

1. Connect a dealer-level scan tool (wiTECH 2) or a capable aftermarket tool like MultiECUScan to the vehicle.
2. Check for all active and stored Diagnostic Trouble Codes (DTCs) in all modules.
3. Using the vehicle's VIN, check for any open recalls or applicable Technical Service Bulletins (TSBs). Specifically search for TSBs 18-045-23, 18-026-20, and 18-101-19.
4. If an applicable TSB for a software update is found and the vehicle's software is outdated, perform the PCM reprogramming as instructed. This is the most likely fix.
5. Clear all DTCs and perform a test drive to see if the U1008 code returns.
6. If the code returns, the next step is to inspect the auxiliary water pump relay (part #06106094AA). It is located in the fuse box behind the driver-side headlight. Swap it with an identical relay (e.g., for the headlamp washer) to see if the fault clears. If it does, replace the relay.
7. If the relay is good, use the scan tool to view the status of all modules on the LIN 1 bus. Identify any module that is not communicating. The most likely culprit is the Charge Air Cooler coolant pump.
8. Inspect the wiring and connectors for the LIN 1 bus, paying close attention to the non-communicating module, checking for any visible damage, corrosion, or loose connections.
9. If wiring is intact, the non-communicating module (likely the CAC pump) is faulty and needs replacement.

Parts You'll Likely Need

• Powertrain Control Module (PCM) Software Update — This is not a physical part, but a service. It is the most common documented fix for the U1008 code on this vehicle, as per multiple manufacturer TSBs.
  OEM price range: $150-$300 (Labor)
  Aftermarket price range: N/A
• Auxiliary Water Pump Relay (OEM #06106094AA) — This relay controls the CAC pump. It is a very common failure point that can cause communication and performance issues with the pump, triggering the U1008 code, sometimes without a check engine light.
  Trusted brands: Mopar
  OEM price range: $20-$40
  Aftermarket price range: $10-$25
• Charge Air Cooler (CAC) Coolant Pump (OEM #50547391) — Also called the auxiliary water pump or intercooler pump, this part is a primary component on the LIN 1 bus and is known to be a point of failure that can cause the U1008 code if a software update and relay replacement do not resolve it.
  Trusted brands: Mopar, Bosch
  OEM price range: $250-$400
  Aftermarket price range: $150-$250

Related Codes That Often Appear With This One

• P026E-00 — This code for 'Charge Air Cooler Coolant Pump Performance' is frequently listed alongside U1008 in TSBs, as the pump is a key component on the LIN 1 bus.
• P015A-00 — An O2 sensor code often grouped with U1008 in TSBs that are resolved with a PCM software update.
• P1CEA-00 — A 'Boost Side EVAP Purge System Performance' code that is also mentioned in the same software update TSBs as U1008.
• P2299-00 — Brake/Accelerator Pedal Position Incompatible code, listed in TSB #18-026-20 as being resolved by the same software update.

Technical Service Bulletins (TSBs) & Recalls

• 18-045-23: Mentions U1008-00 - LIN 1 BUS as one of several codes that may be present and cause inspection failures, addressed by a software update. Also notes the update improves turbo O-ring durability.
• 18-026-20: Lists U1008-00 - LIN 1 BUS among codes that can be set and cause inspection failures, fixed by a PCM software update.
• 18-101-19: Lists U1008-00 - LIN 1 BUS as a code that may cause MIL illumination or driveability issues, resolved by a PCM software update.

Platform-Specific Known Issues

• A series of TSBs released for the 2018-2019 Stelvio (and Giulia) indicate that a group of seemingly unrelated trouble codes, including U1008, are often caused by software glitches in the Powertrain Control Module. The fix is a dealer-installed software update, not a hardware replacement.
• A failing CAC pump relay can cause a 'silent' U1008 code (stored, but with no MIL) that results in a tangible loss of performance, which can be confusing for owners to diagnose without a scan tool.

Mechanic-Grade Diagnostic Values

• LIN Bus Voltage at Rest — expected: Approximately 12 volts (or 1 volt less than system voltage). Failure: Voltage significantly lower than 12V may indicate a short or faulty component pulling the bus down.
• LIN Bus Voltage During Communication (Peak Min/Max) — expected: Max ~12V, Min ~1V. Failure: Readings that do not toggle between the high and low states indicate a communication breakdown. A meter not set to 'peak' min/max may show an average of 7-9V, which is not sufficient for diagnosis.
• Battery Voltage During LIN Bus Diagnosis — expected: Stable voltage between 13.2V and 13.5V (using a battery charger/tender). Failure: Voltage dropping below 13.2V can cause false readings and diagnostic errors.

Hidden / Shadow Codes Worth Checking

• U1008-08: LIN Bus - Bus Signal or Message Failure. This sub-type is a general failure code used when the specific fault cannot be assigned to another sub-type. (see via Advanced scan tools like MultiECUScan or the dealer wiTECH tool can display these 2-digit failure type indicators.)

Scan Tool Commands That Help

• wiTECH 2: Body Control Module (BCM) Proxi Alignment Procedure — This procedure is required after reprogramming the PCM to ensure all vehicle modules correctly recognize each other on the network.
• wiTECH 2: Phonic Wheel Replacement — This routine, located in the ECM's miscellaneous functions, must be performed after the PCM software flash to prevent DTC P1300 (Flywheel Self Learning) from being set.
• MultiECUScan / AlfaOBD: Active Diagnosis / Actuators — These tools allow users to command specific components to turn on, such as the 'Charge air cooler pump'. This can be used to verify if the CAC pump and its relay are functional after a repair or during diagnosis.

Wiring & Ground Locations

• LIN 1 Bus — The LIN 1 bus connects the Powertrain Control Module (PCM) to components including the Charge Air Cooler (CAC) coolant pump and the Engine Oil Level Sensor.. A fault in the wiring (short/open) or a bad connection at any point along this bus will cause a U1008 code. A full wiring diagram is essential for tracing the circuit from the PCM to each component.

Real Owner Repair Stories

• Reddit user in r/AlfaRomeoGiulia (Alfa Romeo Giulia (platform-mate to Stelvio)) — Intermittent U1008-00 'LIN serial line' fault code found using MultiECUScan (MES). The user noted this could lead to high intake air temps.
  ❌ Tried (didn't work) The user went straight to the suspected cause based on forum knowledge.
  ✅ What actually fixed it The owner proactively replaced the auxiliary water pump relay with the superseded Mopar part number 06106094AA to prevent future issues. This is a common preventative fix in the community for this code.

OEM Part Supersession History

• Unknown → 06106094AA (Mopar) — This is the commonly referenced updated part number for the multi-purpose relay used for the auxiliary water pump.
  Heads up: This part may also be cross-referenced or replaced by part number 68367624AA. Another source indicates it was replaced by 6106093AA, so verifying the correct part with a dealer is recommended.