B1370 on 2015-2019 Chevrolet Silverado 2500: Ignition Circuit Fault Causes and Fixes

What's Unique About the 2015-2019 Chevrolet SILVERADO 2500

On the K2XX platform Silverado, code B1370 is a well-documented issue and rarely points to a single failed part. Instead, it's a strong indicator of specific electrical weak points identified in multiple GM Technical Service Bulletins (TSBs). The most common culprits are poor terminal connections at the main fuse blocks or a specific wire, Circuit 5199 (typically pink), that corrodes under the driver's side door sill plate due to moisture ingress. These issues interrupt the critical 'Ignition 1' voltage supplied by the KR73 Ignition Main Relays.

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 or starts and immediately stalls.
• Inoperative HVAC controls.
• No audible feedback (chime) from turn signals.
• Instrument panel gauges fluctuate or are inoperative.
• Check Engine Light (Malfunction Indicator Lamp) does not illuminate when the key is in the 'Run' position before starting.
• "Service 4WD" message may appear on the dash.
• Radio display is blank or does not turn off when the door is opened.
• Relay clicking sound from the dash area while driving.
• Rearview camera inoperative when shifting to reverse.
• Engine continues to run after turning the ignition off, until a door is opened (Note: TSB PIT5391A attributes this specific symptom to a loss of ground to the Ignition Main Relay, not loss of voltage).

Most Likely Causes

1. Damaged/Corroded Wiring Under Driver's Sill Plate 🔴 High Probability TSB #PIT5391 and its revisions specifically identify Circuit 5199 (a pink wire) which runs in a harness under the driver's door sill plate. This area is prone to trapping moisture from wet shoes or weather, causing the wire or its splice (J308) to corrode and create high resistance or an open circuit.
   How to confirm: Remove the driver's side plastic sill plate and peel back the carpet to inspect the wiring harness. Look for a bulge in the harness tape, green or white powder (corrosion), or an obviously broken pink wire. A diagnostic video on a Chevy Express with similar codes showed the break was located under the carpet near where the driver's foot rests.
   Typical fix: Cut out the damaged section of wire and splice in a new piece using weatherproof butt connectors or by soldering and sealing with heat-shrink tubing to prevent future moisture intrusion.
   Est. part cost: $5-$25
2. Poor Terminal Connection at Fuse Block 🔴 High Probability TSB #PIT5391E and PIT5391F identify poor terminal fit, corrosion, or backed-out pins at the Underhood Fuse Block (X50A) and the Left Instrument Panel Fuse Block (X51L) as a primary cause. Vibration and thermal cycles can degrade these critical connections over time. Specific callouts include connector X4, pin M5 for circuit 5199 and connector X2, pin M7 for circuit 439 at the underhood block.
   How to confirm: Disconnect the battery. Unplug the main connectors from the fuse blocks (especially X50A connectors X4 and X2) and visually inspect for any terminals that are pushed out, bent, or show signs of corrosion or heat.
   Typical fix: Carefully reseat the affected terminal using a proper terminal tool. If the terminal is damaged or has poor tension, it must be replaced. This may involve sourcing a replacement terminal and crimping it to the wire. In severe cases of heat damage, the connector pigtail or the entire fuse block may need replacement. 🎬 See how to repair damaged fuse box connectors and wiring.
   Est. part cost: $10-$450
3. Poor Connection at Serial Data Gateway Module (SDGM) 🟡 Medium Probability TSB #PIT5586 and its revisions note that the many symptoms associated with B1370 can be caused by poor terminal connections at the SDGM's X1 or X2 connectors. This module, located above the pedals under the driver's side dash, is a central hub for vehicle communication, and a bad connection can disrupt the entire network.
   How to confirm: Locate the SDGM under the driver's side dash, often behind a plastic vent or felt cover. Disconnect the X1 and X2 connectors and inspect for loose, bent, or backed-out terminals.
   Typical fix: Repair or reseat the affected terminal(s) as needed. In some cases, a software anomaly can cause the SDGM to 'lock up,' which can be temporarily fixed by pulling its fuse (F26DL for trucks) for one minute.

Rare But Worth Checking

• Faulty Ignition Main Relay (KR73): The TSBs mention that the Ignition Main Relays (one in the underhood fuse block, one in the cabin fuse block) could fail to turn on, but this is less common than the wiring and terminal issues that feed them. A faulty relay is a simple and inexpensive part to swap for diagnosis.
🎬 Watch: How to locate and replace the ignition main relay.
• Failed Body Control Module (BCM): While the BCM is the module that sets this code, it is more often the victim of bad inputs than the root cause. All wiring and connection issues detailed in the TSBs should be exhaustively ruled out before condemning the BCM. Replacement requires programming by a dealer or qualified shop.

Diagnosis Steps

1. Scan all vehicle modules and record all present DTCs. Note the presence of multiple U-codes alongside B1370, which strongly suggests a network power issue.
2. Verify the battery is fully charged and the terminals are clean and tight.
3. Check the KR73 Ignition Main Relays and their fuses in both the underhood (X50A) and left instrument panel (X51L) fuse blocks. Consider swapping a relay with a known-good one.
4. Following TSB #PIT5391F, disconnect the battery and carefully inspect the connectors at both fuse blocks for backed-out terminals, corrosion, or damage. Pay close attention to Circuit 5199 (Pink wire) at X50A connector X4, pin M5 and Circuit 439 at X50A connector X2, pin M7.
5. Remove the driver's side door sill plate and peel back the carpet. Inspect the wiring harness for corrosion or breaks, specifically focusing on the pink wire for Circuit 5199 and splice J308.
6. If no issues are found, inspect the X1 and X2 connectors at the Serial Data Gateway Module (SDGM) per TSB #PIT5586E.
7. If all wiring and connections are confirmed to be good, use a multimeter to test the Ignition 1 voltage signal at the BCM connector. If the signal is present and correct, the BCM may be at fault, but this is the last resort.

Parts You'll Likely Need

• Wiring Repair Supplies — The most common fixes involve repairing the corroded pink wire (Circuit 5199) under the sill plate or a terminal at a fuse block connector.
  Trusted brands: 3M
  OEM price range: $10-$30
  Aftermarket price range: $5-$20
• Underhood Fuse Block (OEM #84366378) — If the terminal connections are damaged beyond repair from heat or corrosion, the entire fuse block may need to be replaced. Note: Part number 84766378 appears to be a bumper bracket, not the fuse block. The correct fuse block part number should be verified by VIN.
  Trusted brands: ACDelco

Related Codes That Often Appear With This One

• U0140 — Lost Communication With Body Control Module. This often appears because the BCM is on the receiving end of the faulty ignition circuit or is unable to communicate due to the network disruption.
• U0155 — Lost Communication With Instrument Panel Cluster (IPC). The IPC loses power or data when the ignition signal is lost, causing dead gauges.
• U0164 — Lost Communication With HVAC Control Module. This explains why the climate controls go dead when B1370 is present.
• B1325 — Device Power 3 Circuit Malfunction. This is another power mode-related code that often accompanies B1370, pointing to a systemic electrical issue.
• P0513 — Incorrect Immobilizer Key. This can be set when the BCM and other modules lose power improperly during a start sequence.

Technical Service Bulletins (TSBs) & Recalls

• PIT5586E: Addresses widespread electrical issues including B1370, pointing to terminal issues at the Serial Data Gateway Module.
• PIT5391F: The most relevant TSB, detailing the no-start/stall condition, loss of Ignition 1 voltage, and points directly to checking fuse block terminals and the corroded wire under the driver's sill plate.
• 10-00-89-005: A general GM bulletin referenced by other TSBs for proper wiring and connector repair procedures.

Platform-Specific Known Issues

• TSB #PIT5391F explicitly details the common failure of Circuit 5199 (pink wire) under the driver's sill plate due to corrosion, and poor terminal fit at the X50A and X51L fuse blocks, calling out specific connector pins to check.
• TSB #PIT5586E points to terminal issues at the Serial Data Gateway Module (SDGM) as another potential cause for the cluster of communication codes that accompany B1370.

Mechanic-Grade Diagnostic Values

• Voltage on 'Device Ignition 1' circuit (e.g., Circuit 5199) — expected: Battery Voltage (~12.6V) with Key ON, Engine OFF. 0V with Key OFF.. Failure: 0V or significantly less than battery voltage with Key ON indicates an open circuit or short to ground. Any voltage greater than 0V with Key OFF indicates a short to power.
• Ignition 1 Voltage at Sensing and Diagnostic Module (SDM) — expected: 9-16 volts. Failure: Voltage outside this range indicates a fault in the ignition 1 circuit.

Scan Tool Commands That Help

• GDS2: Module Diagnostics > Body Control Module > Control Functions — To access and perform bidirectional tests on various BCM-controlled subsystems like exterior lighting or power windows to verify if the BCM is capable of commanding functions. This helps isolate whether the fault is in the BCM's command output or downstream components.
• GDS2: Immobilizer Key Programming — After replacing the BCM or other security-related components, the keys will need to be relearned to the vehicle. GDS2 provides the guided function to perform this procedure.

Wiring & Ground Locations

• X50A — Underhood Fuse Block, located in the engine compartment.. This is a primary location for the KR73 Ignition Main Relay and fuses. TSBs specifically point to poor terminal connections at its connectors, like X4 pin M5 and X2 pin M7, as a root cause.
• X51L — Left Instrument Panel Fuse Block, located inside the cabin, typically at the driver's side of the dashboard.. This fuse block also contains a KR73 Ignition Main Relay and is another common point for poor terminal connections that can cause a loss of Ignition 1 voltage.
• Circuit 5199 — A pink wire running in the main harness under the driver's side door sill plate.. This specific circuit is called out in multiple TSBs as being highly prone to corrosion and damage from moisture ingress in the sill plate area, leading to an open circuit for Ignition 1 voltage.
• G103 — Located at the left rear of the engine compartment on the cowl, above the brake booster.. This is a critical ground point for the Body Control Module (BCM), Instrument Panel Cluster (IPC), and Data Link Connector (DLC). A poor connection here can cause widespread communication and power issues, mimicking the symptoms of B1370.
• Driver's A-Pillar Ground — Located inside the cab, behind the driver's side A-pillar trim.. This ground is known to be a failure point and can affect dash and interior electronics. While not the most common cause for B1370, it's a known weak point in the overall electrical system.

Real Owner Repair Stories

• Chevy Express Forum / YouTube (2008 Chevy Express (similar platform and wiring principles)) — No crank, security light on, codes B1370 and B1380.
  ❌ Tried (didn't work) Replaced fuse boxes, Considered replacing the key
  ✅ What actually fixed it A broken and corroded red/white power wire was found under the driver's side floor mat/carpet, near where the driver's foot rests. The wire had rotted from moisture and wear. The fix was to cut out the bad section and splice in a new piece of wire.

Model Year Variations Within This Range

• 2015-2019: For the specific electrical faults related to code B1370 (corroded sill plate wiring, loose fuse block terminals), there are no significant documented variations within the 2015-2019 K2XX generation. The TSBs and common failure points apply consistently across these model years.