P2537 on 2015-2017 GMC Sierra: Ignition Circuit Low Causes and Fixes

What's Unique About the 2015-2017 Gmc SIERRA

On this generation of GMC Sierra and its K2XX platform mates, P2537 is strongly linked to a specific wiring failure documented by GM. Technical Service Bulletin #PIT5308D points directly to an open or high-resistance fault in 'Circuit 5985', which is a violet-colored wire. This wire is known to get damaged in two primary locations: in the harness under the driver's side sill plate or along the left frame rail near the underhood fuse block. 🎬 Watch: How to replace the engine wiring harness junction block. This specific, common failure point makes it a unique issue for this platform compared to generic ignition switch problems on other vehicles.

Diagnostic Flowchart

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

Symptoms You May Notice

• Blower motor stays on after the ignition is turned off (especially on diesel models).
• Check Engine Light is on.
• Dead battery due to parasitic drain from the blower motor or other modules staying awake.
• Remote start is inoperative.
• Power liftgate may not work when the ignition is off.
• Intermittent no-start condition or engine stalls.
• Communication codes with other modules (e.g., U0100, U0074) may be present.
🎬 Watch: How to identify common GM truck electrical and ground issues.

Most Likely Causes

1. Damaged wire in Circuit 5985 🔴 High Probability GM Technical Service Bulletin #PIT5308D specifically identifies a known issue where this circuit develops high resistance or an open. Common failure points are the wiring harness located under the driver's side sill plate or the chassis harness along the left frame rail between the rear body mount and front bed mount. The wire, typically violet, can chafe, corrode, or break in these locations.
   How to confirm: The TSB recommends a load test. Connect a 194 bulb between Circuit 5985 (violet wire) and a good ground. With the BCM awake (ignition on), the bulb should light brightly. If it's dim or doesn't light, an issue exists in the wire. Voltage across the lit bulb should be at least 11V. Key test points are ECM connector X1, pin 43 and TCM connector X1, pin 48.
   Typical fix: Repair the damaged section of the wire. This involves cutting out the bad section, splicing in a new piece of wire using a quality butt connector, and protecting the repair with heat shrink tubing.
   Est. part cost: $5-$20
2. Faulty Ignition Switch 🟡 Medium Probability → Shop Ignition Switch
   How to confirm: If voltage is present and correct at the BCM output for circuit 5985 but the code persists and other circuits are also acting up, the ignition switch itself may be worn. Test the switch's terminals for correct voltage in each key position (Off, Acc, Run, Start). With the key in the ACC position, voltage at the switch connector should be between 11.5V and 12.5V; a reading below 9V points to a switch issue.
   Typical fix: Replace the ignition switch. The ACDelco ignition lock cylinder is part number D1457C.
   Est. part cost: $30-$80
3. Poor Connection or Blown Fuse ⚪ Low Probability
   How to confirm: Visually inspect fuses related to the ignition and body control module in the panels on both sides of the dashboard and under the hood. Check connectors at the BCM, ECM, and TCM for corrosion or loose pins.
   Typical fix: Replace any blown fuses and clean or repair corroded connectors.
   Est. part cost: $1-$15

Rare But Worth Checking

• Faulty Body Control Module (BCM): → Shop Body Control Module If the ignition switch and wiring are confirmed to be good, but there is no voltage being sent out on Circuit 5985 from the BCM, the BCM itself could be the problem. This is an expensive part and should be the last item to consider after all other possibilities are exhausted.

Diagnosis Steps

1. Scan for all DTCs. Note if P2537 is accompanied by other codes like P129D or U-codes.
2. Check for the most common symptom: Does the HVAC blower motor remain on after turning the truck off?
3. Set your multimeter to DC Volts. Connect the black lead to a good chassis ground.
4. With the ignition in the 'RUN' position, locate Circuit 5985 (typically a violet wire) at the ECM connector X1, pin 43 or the TCM connector X1, pin 48.
5. Probe the pin for Circuit 5985 with the red lead. You should see a voltage reading close to battery voltage (12V+).
6. If voltage is low or zero, perform a load test as described in TSB PIT5308D: connect a 194 bulb between the circuit and ground. A dim or unlit bulb confirms high resistance or an open in the wire.
7. If the load test fails, inspect the two most common failure locations. First, remove the driver's side door sill plate and peel back the carpet to expose the wiring channel. Second, inspect the chassis harness along the left frame rail, especially between the rear body mount and front bed mount.
8. Carefully inspect the violet wire (Circuit 5985) for any signs of chafing, corrosion, breaks, or poor previous repairs.
9. If a damaged wire is found, repair it using a quality butt connector and heat shrink tubing.
10. If the wiring appears intact and passes a load test, the issue may be a faulty ignition switch or, rarely, a faulty BCM.

Parts You'll Likely Need

• Wiring Repair Supplies — The most common cause is a damaged wire in Circuit 5985, which requires splicing and repair rather than part replacement.
  Trusted brands: 3M
  Aftermarket price range: $5-$20
• Ignition Switch/Lock Cylinder (OEM #84668679 (Cylinder Kit), D1457C (ACDelco Lock Cylinder)) — If the wiring is confirmed to be good, the internal contacts of the ignition switch may be worn, causing a voltage drop.
  Trusted brands: ACDelco, Standard Motor Products
  OEM price range: $50-$100
  Aftermarket price range: $30-$80

Related Codes That Often Appear With This One

• P129D — This code, for 'Fuel Pump Driver Control Module Ignition On/Start Switch Circuit Low Voltage', is mentioned alongside P2537 in TSB #PIT5308D. Both codes relate to low voltage on critical ignition-on signal circuits, indicating a shared electrical fault in Circuit 5985.
• U0100 — This code for 'Lost Communication With ECM/PCM' can be triggered because the broken Circuit 5985 wire prevents the ECM from 'waking up' and communicating on the vehicle's network.

Technical Service Bulletins (TSBs) & Recalls

• PIT5308D: Addresses symptoms like the blower motor staying on, remote start inoperative, and DTC P2537/P129D, pointing to a fault in Circuit 5985. It provides specific diagnostic procedures, including a load test with a 194 bulb, and identifies known wire failure locations.

Platform-Specific Known Issues

• A known wiring issue in Circuit 5985 (violet wire) is the primary cause for this code on 2015-2017 Sierra models, as documented in GM TSB #PIT5308D.
• There are two primary documented chafe/break points for this wire: under the driver's side sill plate and in the chassis harness along the left frame rail.

Mechanic-Grade Diagnostic Values

• Accessory Wakeup Circuit (5985) Voltage — expected: Approximately 12V (Battery Voltage) when the BCM is awake (e.g., ignition ON).. Failure: The TCM may set DTC P2537 if it detects less than 6 volts for 1 minute.
• Load Test on Circuit 5985 — expected: A 194 bulb connected between the circuit and ground should light brightly, with at least 11 volts measured across the bulb.. Failure: A dim or unlit bulb indicates high resistance or an open. The 194 bulb draws approximately 250mA, and using a larger load can lead to misdiagnosis.
• Circuit 5985 Continuity — expected: Less than 2 ohms of resistance from end to end.. Failure: A reading of 2 ohms or greater indicates high resistance in the circuit requiring repair.

Scan Tool Commands That Help

• GDS2: Data Display: BCM Ignition Accessory/Run parameter — When starting diagnosis, verify with a scan tool that the BCM's 'Ignition Accessory/Run' parameter displays 'Active' when the ignition switch is in the Accessory or Run position. This confirms the BCM is seeing the correct input from the ignition switch before you start testing downstream wiring.
• GDS2: Data Bus Diagnostic Tool — If multiple communication (U-prefix) codes are present with P2537, this tool can be used to identify which control modules are not communicating on the data bus, helping to pinpoint the location of a wiring fault.

Wiring & Ground Locations

• Circuit 5985 — A violet (or sometimes tan) wire running from the BCM to the ECM and TCM.. This is the Accessory Wakeup signal wire. It is the primary point of failure documented in TSB PIT5308D, known to break or corrode under the driver's door sill plate or along the left frame rail.
• BCM Connector X5, Pin 21 — On the Body Control Module (BCM), located on the driver's side of the instrument panel.. This is the source pin for the Circuit 5985 wakeup signal. If voltage is good here but low at the ECM/TCM, the fault is in the wiring between them.
• ECM Connector X1, Pin 43 — The X1 connector on the Engine Control Module (ECM), located in the engine bay.. This is a key destination for Circuit 5985 and a primary test point. Low or no voltage here, when voltage is present at the BCM, confirms a wiring fault.
• TCM Connector X1, Pin 48 — The X1 connector on the Transmission Control Module (TCM).. This is another key destination for Circuit 5985 and a test point. The TCM is often the module that sets the P2537 code when it detects low voltage on this pin.
• G110 / G114 — Body and engine harness grounds located in the engine bay, often on the cylinder head or core support.. While not directly on Circuit 5985, loose or corroded main ground connections can cause widespread, intermittent low voltage issues and electrical problems that could mimic or contribute to a P2537 fault. Ensuring these are clean and tight is a good practice during any electrical diagnosis.

Real Owner Repair Stories

• tahoeyukonforum.com user (2015+ GM SUV (platform mate)) — Blower motor running continuously after the vehicle was shut off, leading to a dead battery.
  ❌ Tried (didn't work) Initial diagnosis was unclear.
  ✅ What actually fixed it The owner followed advice related to TSB PIT5308D and found a broken wire under the driver's side sill plate. Repairing this wire resolved the blower motor issue and the associated trouble codes.