P2537 on 2015-2018 Cadillac Escalade: Ignition Circuit Low Voltage Causes and Fixes

What's Unique About the 2015-2018 Cadillac ESCALADE

The 2015-2018 Escalade shares its K2XX platform with the Chevrolet Tahoe/Suburban and GMC Yukon. For this specific generation, GM issued an updated technical bulletin (PIT5308C) that directly links P2537 to specific, and sometimes confusing, symptoms like the remote start or power liftgate failing. The issue isn't just about the radio not working; it's about a critical communication failure where key modules don't 'wake up' properly when the ignition is on. This is due to a fault in the BCM's accessory power signal on what GM calls Circuit 5985. The bulletin specifically identifies a common chafe point for this circuit under the driver's side door sill plate. A secondary, but critical, issue on this platform is a poor BCM ground at location G218, which can cause identical symptoms.

Diagnostic Flowchart

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

Symptoms You May Notice

• Remote start is inoperative.
• Power liftgate does not work when the ignition is off (but may work when ignition is on).
• Check Engine Light is on.
• Crank but no start, or a start-and-stall condition.
• Accessories like the radio, climate controls, or power windows do not work in the 'ACC' key position.
• Transmission may not shift properly in some cases.
• Blower motor stays on after the engine is turned off.

Most Likely Causes

1. Wiring Fault in Accessory Wakeup Circuit (5985) 🔴 High Probability This specific circuit is cited in GM bulletin PIT5308C. The bulletin identifies a known chafe point for the wiring harness under the driver's side door sill plate for all affected models. Over time, rubbing in this area can damage the wire's insulation, leading to a short or an open circuit.
   How to confirm: Using a voltmeter, check for battery voltage on circuit 5985 (Violet/Yellow wire) at the ECM and TCM connectors with the ignition on. If voltage is low or absent, inspect the wiring harness under the driver's sill plate for damage. The TSB also recommends load testing the circuit with a 194 bulb; if the bulb doesn't light or the voltage drops below 11V with the bulb connected, the wire has high resistance.
   Typical fix: Repair the damaged section of the wire harness. This involves cutting out the bad section, splicing in a new piece of wire, and protecting it with heat shrink tubing.
2. Failing Body Control Module (BCM) 🟡 Medium Probability → Shop Body Control Module The BCM is the source of the accessory wakeup signal. An internal fault in the BCM's driver circuit can prevent it from sending the correct voltage to the other modules. This can also be caused by an external factor, a poor BCM ground at G218.
   How to confirm: If the wiring (Circuit 5985) is confirmed to be physically intact and passes a load test, but there is still no voltage output from the BCM on that pin (Pin 22 on its connector), the BCM itself is the likely culprit. This requires a capable scan tool like GDS2 to check BCM data and status.
   Typical fix: Replace the Body Control Module. This is NOT a plug-and-play part; the new module MUST be programmed to the vehicle's VIN and options using GM's Service Programming System (SPS) or equivalent tool.
   Est. part cost: $250-$500
3. Faulty Ignition Switch ⚪ Low Probability → Shop Ignition Switch While less common than BCM or wiring issues for this specific symptom set on this platform, the ignition switch is a mechanical part that can wear out. Worn contacts can create high resistance, causing a voltage drop.
   How to confirm: Probe the accessory terminal on the ignition switch connector. If the voltage is low here when the key is in the ACC position, the switch is likely faulty.
   Typical fix: Replace the ignition switch.
   Est. part cost: $70-$150

Rare But Worth Checking

• Poor BCM Ground (G218): A well-documented issue on the K2XX platform involves the main ground for the BCM, designated G218. 🎬 Watch: How to locate and fix the G218 ground issue. During assembly, sound-deadening material can get trapped between the ground lug and the chassis, causing high resistance. This leads to erratic BCM behavior and can cause a low voltage output on circuits it controls, like the accessory wakeup circuit. This should be inspected before replacing the BCM, as it can mimic BCM failure.
• Faulty Transmission Control Module (TCM) or Engine Control Module (ECM): It is rare for the receiving module (TCM or ECM) to be the cause of the low voltage reading, but an internal short could theoretically cause the issue. This should only be considered after the BCM, wiring, and ignition switch have been ruled out.

Diagnosis Steps

1. Read all stored DTCs with a scanner capable of communicating with the BCM, TCM, and ECM. Note any other communication codes.
2. Check and record the vehicle's battery voltage to ensure it is at a healthy level (12.4V+). Charge if necessary.
3. Attempt to use the remote start and power liftgate to confirm the symptoms described in TSB PIT5308C.
4. Turn the ignition on (engine off). Access the ECM and TCM connectors.
5. Using a voltmeter, carefully probe the terminal for circuit 5985 (Violet/Yellow wire) at both the ECM and TCM. You should see a voltage close to battery voltage (approx. 12V).
6. If voltage is low or zero, the next step is to load test the circuit. Connect a 194 incandescent bulb between the circuit 5985 terminal and a known good ground. Wake the BCM up (e.g., turn on headlights).
7. If the 194 bulb does not light, there is an open or short-to-ground in circuit 5985. Proceed to inspect the wiring.
8. If the bulb lights, measure the voltage across the lit bulb. If it is less than 11 volts, there is high resistance in the circuit.
9. Inspect the known problem area for the wiring harness: remove the driver's side front door sill plate and carefully examine the harness that runs beneath it for any signs of chafing, pinching, or corrosion.
10. If the wiring is confirmed to be good, inspect the BCM ground G218. It is located under the driver's side dashboard, near the A-pillar and above the speaker. Remove the nut, clean the contact surfaces, ensure no insulation is trapped, and retighten.
11. If the wiring and ground G218 are confirmed to be good, but the voltage output from the BCM on Pin 22 of its connector is still low, the BCM is likely faulty and requires replacement and programming.

Parts You'll Likely Need

• Body Control Module (BCM) (OEM #13587700, 13595894) — The BCM is the source of the accessory wakeup signal. If it fails internally, or has a poor ground, it will not send the required voltage, triggering P2537 and related symptoms. Replacement requires professional programming.
  Trusted brands: ACDelco (Genuine GM)
  OEM price range: $300-$556
  Aftermarket price range: $200-$400
• Ignition Switch — Though less common for this specific code on this platform, a worn ignition switch can cause a voltage drop on the accessory circuit.
  Trusted brands: ACDelco, Standard Motor Products
  OEM price range: $100-$180
  Aftermarket price range: $50-$120

Related Codes That Often Appear With This One

• U0074 - Control Module Communication Bus A Off
• U0137 - Lost Communication With Trailer Brake Control Module
• U18A2 - Accessory Wakeup Serial Data Circuit
• P129D - Fuel Pump Driver Control Module

Technical Service Bulletins (TSBs) & Recalls

• PIT5308C: Remote Start Inoperative / Power Lift-Gate Inoperative / Start And Stall / No Start / Blower Motor Stays On With Ignition Off / SES MIL / DTC P2537 U18A2 U0074 U0137 P129D. This bulletin confirms the symptoms and cause for 2015-2018 Cadillac Escalades and their platform mates, and points to circuit 5985 as the culprit.
• PIT5405C: This bulletin addresses numerous electrical issues (Stabilitrak warnings, blank screens, no start) and identifies a poor BCM ground at G218 as a primary cause. This is highly relevant to P2537 as it can cause the BCM to output low voltage.

Platform-Specific Known Issues

• A known issue, documented in GM Preliminary Information bulletin PIT5308C, directly connects P2537 to inoperative remote start and power liftgate functions on the 2015-2018 Escalade. The cause is identified as the ECM/TCM not receiving the 12-volt accessory wakeup signal from the BCM via circuit 5985. The bulletin specifically calls out inspecting the wiring harness under the driver's sill plate for damage.
• A second widespread issue on this K2XX platform is a poor BCM ground at location G218, under the driver's side dash. Factory-installed sound deadening material can get caught under the ground lug, causing high resistance and a host of bizarre electrical problems that can mimic a failed BCM.

Mechanic-Grade Diagnostic Values

• Accessory Wakeup Circuit (5985) Voltage Drop — expected: ≥ 11.0 Volts. Failure: Voltage drops below 11.0V when load tested with a 194 incandescent bulb, indicating high resistance.
• TCM Fault Threshold for P2537 — expected: ≥ 6.0 Volts. Failure: The TCM detects that the Ignition Accessory/Run circuit is less than 6 volts for 1 minute.
• Wiring Harness Continuity — expected: ≤ 0.1 Ω. Failure: Resistance is higher than 0.1 Ω, indicating a partial break or corrosion in the wire.
• Ground Point Resistance — expected: < 0.05 Ω. Failure: Resistance from the ground lug (e.g., G218) to a clean chassis point is higher than 0.05 Ω, indicating a poor ground connection.

Scan Tool Commands That Help

• GM GDS2 (Global Diagnostic System 2): Data Bus Diagnostic Tool - Detected State — To actively poll all modules on the data bus to see which ones are communicating. For P2537, you would use this to confirm if the ECM and/or TCM are not responding to the BCM's wakeup signal.
• GM GDS2 (Global Diagnostic System 2): BCM Output Controls — To manually command specific BCM outputs on and off, such as the 'Accessory/Run Power Mode' or related relays. This directly tests the BCM's ability to send the wakeup signal, bypassing the ignition switch input.
• GM GDS2 (Global Diagnostic System 2): ECU Upgrade / SPS (Service Programming System) — This function is required after replacing the Body Control Module to program it with the vehicle's correct VIN, software, and option configuration.

Wiring & Ground Locations

• Circuit 5985 — Pin 22 of the BCM connector. The wire color is typically Violet with a Yellow stripe (VT/YE). The harness runs from the BCM, down the driver's side A-pillar, and under the driver's door sill plate towards the rear of the vehicle.. This is the specific 'Accessory Wakeup Serial Data' circuit that fails to power up the ECM/TCM, directly causing code P2537 and the associated symptoms per TSB PIT5308C.
• G218 — Driver's side, under the dash, near the A-pillar and just above/behind the dash speaker. It is a ground stud on the metal body structure.. This is a primary ground for the Body Control Module (BCM). A poor connection here, often due to trapped sound-deadening material from the factory, causes erratic BCM behavior and can lead to low voltage on output circuits, mimicking a failed BCM and triggering P2537.
• Driver's Sill Plate Harness — The main wiring harness that runs along the floor, underneath the plastic driver's side front and/or rear door sill plates.. This is the known chafe point identified in TSB PIT5308C where Circuit 5985 is most likely to become damaged from rubbing, pinching, or corrosion.

Real Owner Repair Stories

• YouTube User Comment on 'G218 Ground Issue Fix' video (2014-2018 GM Truck (Silverado/Sierra platform)) — Flickering dash and headlights, park assist disabled warnings, power steering loss, and the truck completely shutting off when turning.
  ❌ Tried (didn't work) Testing the battery and alternator, which both tested as fine.
  ✅ What actually fixed it Cleaning the G218 ground connection under the driver's side dash. The user commented, 'Man you solved the biggest headache ever! I have spent hours on google trying to figure out the ground issue. After watching your video and 30 minutes it totally fixed my truck!'.

"I Checked Everything" — The Actual Cause

• A technician may perform a continuity and load test on Circuit 5985 from the BCM to the TCM/ECM and find that the wire itself is perfectly fine. However, the code persists. The actual cause can be the BCM's main ground (G218) being compromised. The BCM has enough of a ground to power itself on and communicate with a scan tool, but the ground connection has too much resistance to handle the load of its outputs, causing the voltage on the accessory wakeup circuit to drop and trigger P2537. The circuit tests clean, but the module powering it is 'starved' for ground.

OEM Part Supersession History

• 13587700 → 13595894 — Standard part revision and update by the manufacturer. Part 13595894 is commonly listed for the 2015-2018 model years.
  Heads up: Both parts require programming to the vehicle's VIN and options upon installation. They are not plug-and-play.