P2535: Ignition switch run/start signal reading high

P2535 ignition switch run/start position circuit high

Severity: Monitor

The reference page rates this as moderate, with starting difficulty or poor fuel economy rather than immediate danger.

It gets more serious if:

Inspect soon: Inspect soon if the engine stalls, loses power or the starting problem gets worse.

P2535 in short

P2535 means the computer sees an unexpected high signal from the ignition switch run/start circuit. Blown fuses, corroded or damaged wiring and connectors, a weak battery or charging fault are the usual causes. On some recent GM trucks it follows fuel pump driver module replacement.

The engine computer watches the ignition switch run/start circuit to know the key is on. If that signal reads abnormally high, it sets P2535.

The reference page lists blown fuses or fusible links, corroded, shorted or open wiring, faulty connectors, corroded battery cables, a defective alternator and a damaged battery as common causes. These are electrical supply and wiring checks.

General Motors bulletin PIT6396 says some 2020-2023 Silverado and Sierra trucks can set P2535 with P12A6, P10DA and C111B after the fuel pump driver module is replaced, and that dealers install a diode until engineering has a fix. Only the NHTSA summary was read.

Most likely causes

Cause 1: Blown fuse, or corroded, shorted or open wiring and connectors
Common general cause
Why it ranks here
The source lists fuses or fusible links, damaged wiring and faulty connectors first, and they are the usual way a supply signal goes wrong.
What would change this
Rises if a fuse is open or terminals are corroded. Falls if fuses and wiring test good.
How to test the underhood fuse block (engine compartment fuse box)
Cause 2: Weak battery, corroded battery cables or charging fault
Common general cause
Why it ranks here
The source lists corroded battery cables, a damaged battery and a defective alternator among the causes.
What would change this
Rises if system voltage is low or cables are corroded. Falls if battery and charging tests pass.
Cause 3: Code set after fuel pump driver module replacement (2020-2023 GM trucks)
Supported by vehicle data
Why it ranks here
GM PIT6396 and PIT6396A cover P2535 with P12A6, P10DA and C111B after a fuel pump driver module replacement on 2020-2023 Silverado and Sierra trucks, with a diode as the interim fix. Only summaries were read.
What would change this
Rises if the module was recently replaced on an affected truck. Falls on other vehicles or without a recent replacement.
Cause 4: Faulty ignition switch
Possible — needs testing
Why it ranks here
The reference page lists the ignition switch among the parts often replaced, but it ranks below the simple supply and wiring checks.
What would change this
Rises if the key position signals drop out when the switch is moved. Falls if wiring and fuses check out.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

Step 1: Check the battery, cables and charging voltage, and inspect the fuses related to the ignition circuit.
Low risk
- IfBattery, cables or charging voltage is poor, or a fuse is blown
  It meansRepair that first.
  Points to: Weak battery, corroded battery cables or charging fault
- IfThose are fine
  It meansCheck recent repairs and wiring.
  Go to step 2
Step 2: Ask whether the fuel pump driver module was recently replaced, and inspect the ignition circuit connectors and wiring for corrosion or damage.
Use cautionTool: multimeter
Warning:Disconnect the battery before unplugging connectors or working under the dash.
- IfA 2020-2023 GM truck had the driver module replaced
  It meansGM bulletin PIT6396 applies.
  Points to: Code set after fuel pump driver module replacement (2020-2023 GM trucks)
- IfWiring or a connector is damaged or corroded
  It meansRepair the circuit.
  Points to: Blown fuse, or corroded, shorted or open wiring and connectors
- IfWiring is good and the signal still reads wrong
  It meansTest the ignition switch.
  Points to: Faulty ignition switch

Symptoms

Check engine light
Starting difficulty or poor fuel economy
Stalling or loss of power Gets more serious: stop and have it checked.

How to fix

Step 1: Check the battery terminals and cables for corrosion and tightness.
Step 2: Ask a dealer whether the vehicle has an open bulletin for P2535.

Parts and cost context

Underhood fuse block (engine compartment fuse box):Check fuses first. Labor varies; get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Chevrolet

2020–2022 · Silverado 1500
Supported by vehicle data
GM PIT6396 covers P2535 after fuel pump driver module replacement. Whether it is still current is not verified.

PIT6396Status unverified
P2535, P12A6, P10DA and/or C111B after fuel pump driver module replacement
2020–2023silverado-1500, silverado-2500-hd, silverado-3500-hd · issued June 29, 2025 · NHTSA 11019825
Dealers install a diode while engineering works on a fix.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
PIT6396AStatus unverified
Revision of PIT6396
2020–2023silverado-1500, silverado-2500-hd, silverado-3500-hd · issued August 22, 2025 · NHTSA 11022075
Revised version of the bulletin above.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

GMC

2020–2022 · Sierra 1500
Supported by vehicle data
GM PIT6396 covers P2535 after fuel pump driver module replacement. Whether it is still current is not verified.

PIT6396 (GMC)Status unverified
P2535, P12A6, P10DA and/or C111B after fuel pump driver module replacement
2020–2023sierra-1500, sierra-2500-hd, sierra-3500-hd · issued June 29, 2025 · NHTSA 11019825
Dealers install a diode while engineering works on a fix.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
PIT6396A (GMC)Status unverified
Revision of PIT6396
2020–2023sierra-1500, sierra-2500-hd, sierra-3500-hd · issued August 22, 2025 · NHTSA 11022075
Revised version of the bulletin above.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

All Charging and starting codes

P2535 questions

Is P2535 high or low?

The code name is circuit high, meaning the computer sees an unexpected high signal. The causes are mostly fuses, wiring, battery and charging faults.

Sources and review

Guide to P2535 OBD error code — PartsAvatar
GM bulletin PIT6396: SES MIL with P2535, P12A6, P10DA and/or C111B after replacing the fuel pump driver module (2020-2023 Silverado and Sierra HD, 2020-2022 1500) — GM (via NHTSA manufacturer communications flat file) , June 29, 2025
GM bulletin PIT6396A: Revision of PIT6396 — GM (via NHTSA manufacturer communications flat file) , August 22, 2025

Last reviewed: October 16, 2026
Written by: Saurabh K.
Editorial review: Pending
Technician review: Technician review pending

This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error

Severity: Monitor

Most likely causes

Cause 1: Blown fuse, or corroded, shorted or open wiring and connectors

Cause 2: Weak battery, corroded battery cables or charging fault

Cause 3: Code set after fuel pump driver module replacement (2020-2023 GM trucks)

Cause 4: Faulty ignition switch

What to test first

Step 1: Check the battery, cables and charging voltage, and inspect the fuses related to the ignition circuit.

Step 2: Ask whether the fuel pump driver module was recently replaced, and inspect the ignition circuit connectors and wiring for corrosion or damage.