B1370 on 2015-2020 Cadillac Escalade: Ignition Circuit Fault Causes and Fixes

What's Unique About the 2015-2020 Cadillac ESCALADE

The 2015-2020 Escalade belongs to GM's K2XX platform. For this specific generation, Technical Service Bulletins (TSBs) like PIT5391A and its successors strongly point to a known issue with poor terminal connections within the underhood fuse block (X50A) and the left instrument panel fuse block (X51L). Before suspecting expensive components like the BCM or ignition switch, diagnosis on these vehicles should always start by inspecting the large connectors (e.g., X2, X4) at the fuse blocks for backed-out or corroded terminals, as this is a well-documented and highly probable cause of B1370.

Diagnostic Flowchart

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

Symptoms You May Notice

• No crank, no start condition.
• Engine starts and immediately stalls.
• Check Engine Light (Malfunction Indicator Lamp) does not illuminate when the key is turned to 'ON'.
• Audible clicking from relays while driving or during a start attempt.
• HVAC controls may be inoperative.
• Turn signals may not produce audible feedback (but external lights may still work).
• Various warning lights may illuminate on the instrument cluster.
• Service 4WD message on instrument cluster.
• Rearview camera inoperative when shifting to reverse.

Most Likely Causes

1. Poor Terminal Connection at Underhood Fuse Block (X50A) 🔴 High Probability As identified in GM TSB PIT5391A and its later revisions, these vehicles are known to have issues with terminals backing out or developing poor connections at the main fuse block connectors. This interrupts the Ignition 1 voltage after the relay.
   How to confirm: Disconnect the battery. Unplug the large connectors (specifically check X2 and X4) from the bottom of the underhood fuse block (X50A) and inspect for any terminals that are pushed back, bent, or show signs of corrosion. TSBs specifically mention terminal M7 in connector X2 (for circuit 439) and terminal M5 in connector X4 (for circuit 5199) as common culprits.
   Typical fix: Reseat the backed-out terminal securely in its connector using a proper terminal tool. If the terminal is damaged or corroded, it will need to be replaced with a new terminal and the wire repaired. In some cases, the entire fuse block may need replacement if the damage is extensive.
   Est. part cost: $5-$50 for a new terminal and wiring repair supplies, $300-$500 for a new fuse block.
2. Failed Ignition Main Relay (KR73) 🟡 Medium Probability The TSB mentions two KR73 relays that supply power to the Ignition 1 circuits, one in the underhood fuse block and one in the left instrument panel fuse block. Like any relay, they can fail over time.
   How to confirm: Locate the KR73 relays in the underhood (X50A) and left instrument panel (X51L) fuse blocks. Swap the suspect relay with an identical one from a non-critical circuit (like the horn) and see if the problem is resolved.
   Typical fix: Replace the faulty relay. The common ACDelco part is a gray, 4-terminal relay.
   Est. part cost: $15-$40
3. Damaged Wiring or Open Circuit ⚪ Low Probability TSB PIT5391A notes that wiring under the driver's sill plate (specifically circuit 5199) can become damaged or corroded, causing an open. Wires can also break anywhere along the harness due to chafing or stress, sometimes near the fuse block itself.
   How to confirm: Perform a continuity test on the Ignition 1 circuit wire (e.g., circuit 439 or 5199) between the fuse block and the BCM. Check for voltage at the relevant fuses with the key in the 'ON' position. Visually inspect the harness under the driver's side sill plate for any signs of water intrusion or corrosion.
   Typical fix: Repair the broken or shorted section of wire. This may involve splicing in a new section of wire and ensuring it is properly sealed from moisture.
   Est. part cost: $5-$25 for wiring repair supplies.
4. Faulty Body Control Module (BCM) ⚪ Low Probability
   How to confirm: This should only be considered after all other possibilities (wiring, fuses, relays, connections) have been exhaustively tested and ruled out by a qualified technician using a scan tool to monitor BCM data.
   Typical fix: Replace the BCM and have it programmed to the vehicle by a dealer or qualified shop with the correct software.
   Est. part cost: $300-$600

Rare But Worth Checking

• Faulty Ignition Switch: While possible, the known TSBs for this platform make fuse block and wiring issues a much more likely starting point. The ignition switch sends the initial signal to the BCM, so a failure can cause this code, but it's less common than the connection problems.

Diagnosis Steps

1. Read all Diagnostic Trouble Codes (DTCs) from all modules. Note any other codes that appear with B1370, especially B1325, U0140, and P0650.
2. Check the symptoms. Confirm if you have a no-crank, start-and-stall, or an inoperative Check Engine Light during the bulb check.
3. Inspect the KR73 Ignition Main Relays. There is one in the underhood fuse block (X50A) and another in the left instrument panel fuse block (X51L). Swap them with known-good relays to test.
4. Crucial Step: Disconnect the negative battery terminal. Unplug the connectors from the underhood fuse block (X50A). Carefully inspect every terminal for signs of corrosion, damage, or being pushed out of the connector housing. Pay close attention to connectors X2 and X4, specifically pins like M7 and M5. This is the most likely cause.
5. If terminals are loose, use a proper terminal tool to reseat them. If corroded, clean or replace them. A terminal pigtail may be required for repair.
6. Inspect the connectors at the Left I/P Fuse Block (X51L) for similar terminal issues, as noted in TSB PIT5391A.
7. If fuse block connections are good, inspect the wiring harness under the driver's side sill plate for corrosion or damage, particularly for circuit 5199.
8. If all wiring and connections test good, use a multimeter to check for voltage at the Ignition 1 fuses with the key on. If fuses are good but have no power, the issue is upstream (relay or fuse block). If they have power, the issue is downstream (wiring to the module or the module itself).
9. If all else fails, the fault may lie with the Body Control Module (BCM), which would require professional diagnosis.

Parts You'll Likely Need

• Underhood Fuse Block Terminal/Pigtail (OEM #e.g., ACDelco 84785110 (representative pigtail)) — This is the most common failure point according to GM service bulletins for this platform, causing an open in the Ignition 1 circuit. The original terminal backs out or corrodes.
  Trusted brands: ACDelco
  OEM price range: $10-$30
  Aftermarket price range: $5-$20
• Ignition Main Relay (KR73) (OEM #ACDelco D1786C (GM 19116057 / 13500114)) — This relay controls power to the Ignition 1 circuit and can fail, causing an open circuit and triggering B1370. There are two on the vehicle.
  Trusted brands: ACDelco, Standard Motor Products
  OEM price range: $25-$40
  Aftermarket price range: $15-$30
• Underhood Fuse Block (X50A) — If the terminal sockets within the fuse block are damaged beyond repair from heat or corrosion, the entire fuse block assembly must be replaced to ensure a reliable connection.
  Trusted brands: ACDelco
  OEM price range: $300-$500
  Aftermarket price range: $200-$400

Related Codes That Often Appear With This One

• B1325 — This code relates to device power voltage, and often appears with B1370 due to the same underlying loss of ignition voltage. It is explicitly mentioned alongside B1370 in TSB PIT5391A.
• U0140 — This code indicates a loss of communication with the Body Control Module (BCM). If the BCM loses its own ignition power source (which B1370 indicates), it can't communicate with other modules, triggering this code.
• P0650 — This code is for a malfunction in the Malfunction Indicator Lamp (MIL) control circuit. TSB PIT5391A links this code with B1370, as the loss of ignition voltage can prevent the instrument cluster from properly powering the check engine light.
• C0364 / U0403 — On 4WD models, these codes for the transfer case control module may appear along with a 'Service 4WD' message, as the TCCM also loses its Ignition 1 power source. This is noted in TSB PIT5391A.

Technical Service Bulletins (TSBs) & Recalls

• PIT5391A / PIT5391F: Addresses a no crank/start-and-stall condition linked to B1370, pointing to a loss of Ignition 1 voltage caused by terminal issues at the X50A and X51L fuse blocks or damaged wiring under the driver's sill plate.
• PIT5586B / PIT5586G: Lists B1370 among many communication and body control codes that can appear when network issues are present, causing symptoms like inoperative HVAC and no audible turn signal feedback. Points to checking SDGM connectors.

Platform-Specific Known Issues

• A known issue documented in TSB PIT5391A and its successors involves poor terminal fit at the underhood fuse block (X50A) connectors, leading to a loss of Ignition 1 voltage and setting code B1370.

Mechanic-Grade Diagnostic Values

• Voltage on Ignition 1 circuit at BCM connector — expected: System voltage (9-16V) with key in RUN or START position.. Failure: Voltage is less than 9V or does not match system voltage, indicating an open or high resistance.
• Voltage on Ignition 1 circuit at BCM connector with key OFF — expected: Less than 1.0 V.. Failure: Voltage is greater than 1.0 V, indicating a short to voltage.
• Resistance of Ignition 1 circuit — expected: Less than 1.0 ohm between the BCM connector and the ignition switch connector.. Failure: Resistance is greater than 1.0 ohm, indicating high resistance or an open in the circuit.

Hidden / Shadow Codes Worth Checking

• B1370 06: Device Ignition 1 (ON and START) Circuit Short to Ground or Open. This is the most common subtype for this issue, indicating the BCM has lost the expected voltage signal. (see via A professional scan tool capable of reading GM body codes and their symptom bytes.)
• B1370 01: Device Ignition 1 (ON and START) Circuit Short to Battery. This indicates the BCM is seeing voltage on the Ignition 1 circuit when it shouldn't, such as when the key is OFF. (see via A professional scan tool capable of reading GM body codes and their symptom bytes.)

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): BCM Data Display > Power Mode — To verify if the BCM's interpretation of the power mode (e.g., 'Run', 'Crank') matches the physical ignition switch position. A mismatch confirms a fault in the input circuits.
• General Maintenance: BCM Reset via Battery Disconnect — After repairing a short circuit, the BCM may internally disable the affected driver circuit to protect itself and will not clear the DTC. A hard reset by disconnecting the battery for at least 30 seconds is required to make the BCM attempt to drive the circuit again and validate the repair.

Wiring & Ground Locations

• X50A — Underhood Fuse Block, located in the engine compartment.. This is the primary hub for the KR73 Ignition Main Relay and the starting point for the Ignition 1 voltage circuits. TSBs point to this as the most common failure area.
• X50A Connector X2, Pin M7 — A specific terminal within a large connector on the underside of the underhood fuse block.. This terminal carries Ignition 1 voltage on circuit 439. It is explicitly called out in TSB PIT5391A as a frequent point of failure due to being backed out or corroded.
• X50A Connector X4, Pin M5 — A specific terminal within a large connector on the underside of the underhood fuse block.. This terminal carries Ignition 1 voltage on circuit 5199. It is explicitly called out in TSB PIT5391A as a frequent point of failure.
• X51L — Left Instrument Panel Fuse Block, located inside the vehicle, typically on the driver's side of the dashboard.. This fuse block contains the second KR73 Ignition Main Relay and is another potential location for terminal issues.
• Circuit 5199 (Sill Plate) — Wiring harness running under the driver's side door sill plate.. This circuit is known to be susceptible to water intrusion and corrosion in this area, leading to an open circuit and causing a no-start condition with code B1370.
• G218 — Under the driver's side dash, near the A-pillar, often behind the dash speaker.. This is a primary ground for the Body Control Module (BCM). A poor connection here, often caused by sound-deadening material trapped under the ground lug from the factory, can cause a wide range of electrical issues, including the BCM misinterpreting data and setting codes like B1370.

Real Owner Repair Stories

• YouTube channel 'Global Commerce CA' (2008 Chevy Express (similar GM electrical architecture)) — No crank, no start, security light stays on, codes B1370 and B1380 present.
  ❌ Tried (didn't work) Replacing the key, Replacing fuse boxes
  ✅ What actually fixed it A broken red and white wire (Ignition 1 circuit) was found in the harness under the carpet, near where the driver's foot rests by the brake pedal. The wire had worn through over time. Repairing the broken wire by splicing it solved the issue.
• YouTube channel 'Diagnose It Right' (2017 Chevy Express Van) — No start, security light behavior indicated an issue, codes B1370 and B1380 were stored.
  ❌ Tried (didn't work) Vehicle had been to a dealer and another shop who could not diagnose it.
  ✅ What actually fixed it A blown 2-amp fuse in the ignition circuit was found and replaced. This simple fix resolved the no-start condition immediately.