P1682 on 2008-2014 Cadillac CTS: Ignition Circuit Fault Causes and Fixes

What's Unique About the 2008-2014 Cadillac CTS

The second-generation Cadillac CTS, built on the GM Sigma II platform, uses a dual-circuit design to provide redundant power verification to the ECM. This design is intended as a failsafe but can be a point of failure. The issue is rarely the expensive ECM itself but is almost always found in the supporting power delivery components like relays, fuses, or the fuse block terminals. These terminals are known to suffer from 'fretting corrosion,' a condition where micro-vibrations cause oxidized debris to build up, creating high resistance. This is a well-documented issue across many GM platforms of the era and is addressed in GM Technical Service Bulletin #09-06-03-004G, which recommends using a specific dielectric grease (Nyogel 760G) to prevent recurrence.

Symptoms You May Notice

• Engine will crank but not start
• Engine will not crank at all
• Check Engine Light is on
• Reduced Engine Power mode is activated
• Engine stalls intermittently, sometimes when hot
• Engine does not turn off when the key is removed
• Various warning lights on the instrument cluster, such as 'Service Traction Control' or 'Service StabiliTrak'
• Key may become stuck in the ignition

Most Likely Causes

1. Faulty Powertrain or Run/Crank Relay 🔴 High Probability → Shop Wiring Relay Relays are electromechanical switches that wear out over time. They are a very common failure point for this code across many GM vehicles.
   How to confirm: Locate the powertrain (labeled 'PWR/TRN') and run/crank relays in the underhood fuse box. Swap the suspect relay with an identical one from a non-essential circuit (like the horn or rear defogger) and see if the car starts and the code clears.
   Typical fix: Replace the faulty relay. It is inexpensive and simply plugs into the fuse box. The common part is a standard 5-pin gray relay.
   Est. part cost: $10-$30
2. Poor Connection at Fuse Block (Fretting Corrosion) 🔴 High Probability The terminals that hold the fuses and relays in the Underhood Bussed Electrical Center (UBEC) can lose tension or develop fretting corrosion, leading to high resistance or an open circuit. This is a widely documented GM issue, and a resistance of just 5-6 ohms 🎬 See how a mobile mechanic repairs these fuse box terminals. in the circuit can trigger the code.
   How to confirm: Disconnect the battery. Unbolt and lift the fuse block to inspect the large connectors on the underside. Look for any signs of discoloration, burn marks, or corrosion on the pins and terminals. Wiggling the powertrain relay while attempting to start may temporarily establish a connection.
   Typical fix: Cleaning the terminals and applying a small amount of dielectric grease (specifically Nyogel 760G as recommended by GM TSB #09-06-03-004G) can be a lasting repair. If terminals are burnt or have lost tension, the fuse block itself may need to be replaced. 🎬 Watch this walkthrough on replacing a GM fuse box.
   Est. part cost: $10 for cleaning supplies/grease, $200-$500 for a fuse block replacement
3. Blown Fuse 🟡 Medium Probability A short circuit in an associated system or a voltage spike can cause a fuse to blow as designed to protect the circuit.
   How to confirm: Visually inspect the fuses related to the ECM, ignition, and powertrain circuits (e.g., 'ECM', 'IGN', 'PWR/TRN'). Use a multimeter or test light to confirm continuity across each fuse.
   Typical fix: Replace the blown fuse. If the new fuse blows immediately, there is an underlying short circuit that must be diagnosed.
   Est. part cost: $1-$5
4. Faulty Ignition Switch ⚪ Low Probability → Shop Ignition Switch
   How to confirm: This requires more in-depth electrical testing of the ignition switch's output circuits using a multimeter and a wiring diagram to ensure it is sending correct voltage signals in each key position. While a common cause on other GM models, it's less frequently the primary culprit for the CTS compared to relays and the fuse block.
   Typical fix: Replace the ignition switch, which is typically located in the steering column.
   Est. part cost: $40-$150

Rare But Worth Checking

• Wiring Harness Damage: An open or short in the wiring between the fuse block and the ECM can cause this code. TSB 21-NA-032 points to a compromised wire crimp inside the X3 connector at the fuse block on some GM vehicles, which can be difficult to see without disassembly. Water intrusion into headlamp assemblies has also been known to short circuits that feed the fuse block, causing this code intermittently in wet weather, as noted in TSB PIT5546G.
• Faulty Engine Control Module (ECM): → Shop Engine Control Module (ECM) This is the least likely cause. The ECM should only be suspected after all other possibilities—relays, fuses, wiring, and the fuse block—have been thoroughly ruled out. Often, other communication codes (U-codes) will be present if the ECM is failing.

Diagnosis Steps

1. Connect a scan tool and verify that P1682 is present. Note any other codes, especially P0685, P0689, or P0101, and diagnose them first if present.
2. Check the battery. Ensure it is fully charged and passes a load test. A weak battery can cause numerous electrical issues, but is not the direct cause of P1682.
3. Locate the underhood fuse block (UBEC). Identify the fuses and relays for the powertrain ('PWR/TRN') and run/crank circuits. Your owner's manual will have a diagram.
4. Inspect the relevant fuses (often labeled 'ECM', 'IGN', 'CRNK') for being blown. Replace if necessary.
5. Swap the powertrain relay and run/crank relay with an identical, known-good relay (GM P/N 13500114 or equivalent) from a non-critical system. Attempt to start the vehicle. If it starts, the relay you moved is faulty.
6. If relays and fuses are good, disconnect the battery. Unbolt and lift the fuse block to inspect the large connectors on the bottom side for signs of corrosion, discoloration (from heat), or loose-fitting pins (fretting). This is a very common failure point.
7. If the problem persists, use a scan tool that can display live data. Monitor the 'Ignition 1 Voltage' and 'EC Ignition Relay Feedback' parameters. The circuit showing significantly lower voltage (more than a 3V difference) is the one with the fault.
8. Based on the scan tool data, trace the wiring for the faulty circuit from the fuse block to the ECM, checking for opens, shorts, or high resistance with a multimeter. Pay close attention to the connector pins at the fuse block.
9. If all wiring and components test good, the final possibility is a fault within the Engine Control Module (ECM) itself, though this is rare.

Parts You'll Likely Need

• Powertrain Relay / Run-Crank Relay (OEM #13500114) — This is the most common failure point for code P1682. These relays control the two ignition voltage signals that the ECM monitors. This part number is a widely used multi-purpose relay in GM vehicles.
  Trusted brands: ACDelco, Standard Motor Products, Bosch
  OEM price range: $20-$40
  Aftermarket price range: $10-$25
• Automotive Fuse — A blown fuse in one of the ignition circuits will cause a voltage mismatch and set this code.
  Trusted brands: Bussmann, Littlefuse
  OEM price range: $1-$5
  Aftermarket price range: $1-$5

Related Codes That Often Appear With This One

• P0685 — This code relates to the ECM/PCM Power Relay Control Circuit. Since P1682 involves the powertrain relay, a fault in the relay's control circuit can trigger both codes.
• P0689 — This code indicates a low voltage condition in the ECM/PCM Power Relay Sense Circuit. It is directly related to the power monitoring that also triggers P1682 and often points to the same root causes like a bad relay or fuse block connection.
• P0101 — This MAF sensor code can appear with P1682 not because the MAF is faulty, but because a wiring issue in the fuse block (specifically connector X3, pin H6 on some models) affects both circuits. Do not replace the MAF sensor if P1682 is also present.

Technical Service Bulletins (TSBs) & Recalls

• TSB #09-06-03-004G: Addresses intermittent no-start and various electrical issues caused by fretting corrosion on connector terminals. It recommends applying Nyogel 760G dielectric lubricant as a corrective action.
• TSB 21-NA-032: While for newer trucks, it's relevant as it describes how a compromised wire crimp in a fuse block connector (X3-H6) can cause P1682 and P0101 simultaneously, highlighting the importance of inspecting the fuse block wiring itself.
• TSB PIT5546G: Documents how water intrusion into headlamp assemblies can backfeed voltage into switched ignition fuses, causing modules to stay awake and setting codes like P1682.

Platform-Specific Known Issues

• Underhood Fuse Block (UBEC) Terminal Fretting: → Shop Fuse Box The most prevalent issue for P1682 on this platform is not the components themselves, but the connections to them. The terminals within the UBEC, particularly for the powertrain relay, are susceptible to fretting corrosion. This creates high resistance, leading to a voltage drop that the ECM detects as a fault. The fix often involves cleaning the terminals and applying dielectric grease, or in severe cases, replacing the fuse block. This is documented in GM service bulletins and is a known issue across their vehicle lineup from this era.

Mechanic-Grade Diagnostic Values

• Voltage difference between 'Ignition 1 Voltage' and 'EC Ignition Relay Feedback' on a scan tool — expected: Less than 3.0 Volts. Failure: A difference greater than 3.0 Volts for more than 1 second will set the code.
• Resistance in either Ignition 1 voltage circuit — expected: Less than 5.0 Ohms. Failure: A resistance of 5.0 Ohms or greater is sufficient to cause the DTC to set.
• System Voltage (Key On) — expected: Greater than 12.4 Volts. Failure: Diagnosis of P1682 should not be attempted if system voltage is below 9V, as it can cause erroneous codes. The DTC will not run if system voltage is below 5.23V.

Scan Tool Commands That Help

• GDS2 / Tech2: Output Control: Powertrain Relay ON/OFF — Use this bidirectional command with the key on, engine off to manually activate and deactivate the powertrain relay. You should hear or feel the relay click with each command, which helps confirm if the ECM's control over the relay is functional.

Wiring & Ground Locations

• Underhood Fuse Block (UBEC) — Located on the passenger side of the engine compartment.. This is the central hub for the powertrain and run/crank relays and fuses. The majority of P1682 faults originate here, either from faulty relays or, more commonly, from poor connections (fretting) at the relay terminals or in the main connectors underneath.
• G102 — On the right front of the engine compartment for a 2011 CTS. On other GM models, it may be at the left rear of the engine.. This is a primary ground point for the Engine Control Module (ECM). A poor ground here can cause a host of electrical issues, including erratic voltage readings that could contribute to a P1682 code.
• UBEC Connectors (e.g., X3) — Large multi-pin connectors on the underside of the Underhood Fuse Block.. These connectors are the interface between the vehicle's wiring harness and the fuse block. They are a known point of failure due to fretting corrosion or loose retaining bolts. TSB 21-NA-032 specifically points to a bad crimp at pin H6 of the X3 connector on some GM models as a cause for P1682.

Real Owner Repair Stories

• YouTube user 'coverman66' (GM vehicle (Trailblazer SS) with similar fuse box design) — Car would stall when hot and then crank but not start. Codes P1682 and P0689 were present.
  ❌ Tried (didn't work) Initial diagnosis pointed towards a possible bad ECM or relay.
  ✅ What actually fixed it The entire underhood fuse box was replaced. The owner noted this is a common problem where the fuse panel overheats and causes internal connection failures, leading to the stall and no-start condition.
• YouTube user 'Chad Barnes' (2008 Pontiac G6 with 2.4L Ecotec engine) — Intermittent no-start which eventually became a permanent crank-no-start. Code P1682 was present.
  ❌ Tried (didn't work) Checking grounds and basic connections.
  ✅ What actually fixed it After disassembling the underhood fuse block, the owner found that the female terminals for one of the relays were spread apart and not making a solid connection. Squeezing the terminals back together to ensure a tight fit on the relay pins solved the problem permanently.

OEM Part Supersession History

• Multiple (e.g., 12135034, 12193606, 19116057) → 13500114 — Part consolidation and potential design updates over many years and vehicle models.
  Heads up: While 13500114 is the correct and widely used gray 5-pin relay for this application, always verify the part number with a VIN. In some rare cases, an incorrect cross-reference in a parts store system could lead to being given a physically different relay.

Model Year Variations Within This Range

• 2008-2014: While the diagnostic principle for P1682 remains the same, the physical layout and labeling of fuses/relays in the underhood and trunk fuse boxes may have minor variations between early (2008-2009) and later (2010-2014) models of the second-generation CTS. Always refer to the owner's manual or fuse box lid for the specific vehicle year.

Diagnostic Flowchart

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used Underhood Fuse Block (UBEC) from a junkyard can be a cost-effective solution, as a new OEM unit can be expensive. The part does not require programming, making it a direct swap. Relays are inexpensive new, so buying used is not recommended.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• Inspect the donor vehicle for signs of front-end collision or water damage. Avoid any fuse block from a car with a flooded interior or engine bay.
• Remove a few relays and fuses to inspect the terminals. Look for bright, clean metal. Avoid any unit with signs of white/green corrosion, black burn marks, or melted plastic.
• Check the underside where the main harness connectors plug in. The plastic should be clean and free of discoloration from heat or moisture.
• If possible, choose a donor vehicle from a dry climate to minimize the risk of pre-existing corrosion.

OEM-only on this vehicle (don't cheap out):

• Engine Control Module (ECM) - While rarely the cause, if the ECM must be replaced, a new or professionally remanufactured unit programmed to the vehicle's VIN is required.

Aftermarket brands forum-validated for this vehicle:

• Relays: ACDelco (OEM), Standard Motor Products (SMP), Bosch.
• Fuse Block: Dorman may offer a replacement, but an OEM unit (new or used) is generally preferred for fit and quality.

Brands owners have reported issues with on this vehicle:

• Unknown, no-name brand electrical components from online marketplaces should be avoided due to potential quality control issues.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0685 — ECM/PCM Power Relay Control Circuit/Open. This code is frequently seen with P1682 as both point directly to a fault in the powertrain relay or its circuit, which is a primary cause of P1682 on the CTS.
• P0689 — ECM/PCM Power Relay Sense Circuit Low. Often appears with P1682 because a faulty relay or poor connection in the fuse block will affect both the main power supply and the feedback (sense) circuit that the ECM monitors.
• P0101 — Mass Air Flow (MAF) Circuit Range/Performance. According to TSB 21-NA-032, a compromised wire crimp within the fuse block can cause both P1682 and P0101 to set simultaneously, indicating a shared electrical root cause.
• P0443 — EVAP Purge Control Valve Circuit. Can appear alongside P1682 when there is a widespread internal failure or heat damage within the underhood fuse block, affecting multiple unrelated circuits powered by it.
• U0100 — Lost Communication With ECM/PCM. P1682 indicates a problem with the ECM's power supply. If the ECM loses power, it cannot communicate with other modules on the vehicle's network, causing them to log this communication code.

Frequently Asked Questions