P135A on Chevrolet: How to Diagnose & Fix
Ignition Coil Supply Voltage Circuit Bank 1
1 Chevrolet model · 1 documented issue · 1 critical · $150-$900 repair
P135A on Chevrolet by model: symptoms, diagnosis and fix
Many second-gen Traverse owners experience random no-crank / no-start events, sometimes after the engine shuts off while driving. GM service bulletins identify two patterns: bent or backed-out terminals at body connector X203 causing loss of communication on the HSLAN data bus with multiple stored DTCs, and a separate intermittent no-crank condition on certain 2019 3.6L LFY models built before February 22, 2019, flagged by ignition coil supply and ignition relay feedback codes and caused by loose terminal tension in the underhood fuse block. The result is being stranded with a vehicle that will not respond to the start button.
Common Symptoms
- Intermittent no-crank when pressing start
- Engine shuts off while driving then won't restart
- Multiple unrelated warning lights / loss of communication
- Sometimes restarts after sitting
How to Fix
Have a technician scan for HSLAN/loss-of-communication DTCs and inspect/repair connector X203 for bent or damaged terminals per the GM bulletin; the second bulletin (19-NA-119) addresses the no-crank codes by voltage-drop testing the underhood fuse block (X50A), repairing loose terminals, and replacing the fuse block if the drop exceeds specification. Owners should also rule out the simpler offenders first — loose/corroded battery terminals, a weak main battery, and a dead key-fob battery, all of which mimic the same symptom.
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Sources for this issue (2)
P135A code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P135A mean on a Chevrolet?
P135A stands for "Ignition Coil Supply Voltage Circuit Bank 1." General Motors code (also used by Saab on GM-based engines), documented across Chevrolet, GMC, Buick, and Cadillac applications. The ignition system uses one coil per cylinder, and the engine control module monitors the power feed from the fuse to those coils. Per GM service information, the code sets when the ECM detects less than about 2.5 volts on the bank 1 ignition coil supply voltage circuit. Without proper coil supply voltage, spark on those cylinders is weak or absent, so the driver typically gets a check engine light, rough running, misfire, hard starting, or a no-start. It is usually a power-supply or wiring problem rather than a bad coil itself, so testing the feed before replacing parts saves money. On Chevrolet it is documented across 1 model: Traverse.
What are the most common causes of P135A?
The most common causes of P135A are: Blown ignition coil fuse or faulty relay feeding the coil supply circuit, Open, chafed, or corroded wiring in the coil supply harness, Corroded or backed-out connector at the ignition coil pack or harness junction, Poor engine or ECM ground causing voltage drop, Shorted ignition coil pulling down the shared supply circuit, Faulty engine control module driver or internal supply circuit (least common). The specific cause varies by vehicle.
How much does it cost to fix P135A on a Chevrolet?
Published repair estimates on Chevrolet range from $150 to $900 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.