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DTC codes / P25xx · Vehicle speed, idle control and auxiliary inputs / P2535

P2535Ignition Switch Run/Start Position Circuit High

P2535 means the ignition switch run/start position circuit is reporting a high voltage condition, which the computer interprets as an unexpected voltage on the sense wire when the switch is not commanding that state. The powertrain control module (PCM) monitors this circuit to confirm the ignition switch is in the correct position for starting and running, and it sets the code when the voltage exceeds the expected threshold.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

  • The engine may not crank or may crank intermittently when the key is turned to start
  • The engine may start but stall immediately or run rough due to incorrect ignition switch signals
  • The warning light (check engine or service vehicle soon) illuminates on the dashboard
  • Other electrical accessories may behave erratically, such as radio or interior lights staying on
  • The vehicle may fail to enter or exit certain modes, like accessory or off, leading to battery drain
  • Often no symptoms besides the warning light, especially if the fault is intermittent

Common causes, most likely first

  1. Faulty ignition switch internal contacts causing a high voltage on the run/start sense circuit
  2. Shorted or chafed wiring in the run/start circuit, often near the steering column or under the dash
  3. Corroded or loose electrical connectors at the ignition switch or PCM
  4. A defective PCM or body control module (BCM) not properly interpreting the switch signal
  5. Aftermarket accessories improperly tapped into the ignition circuit, causing voltage backfeed
  6. A weak or failing battery or charging system causing voltage spikes that trigger the code

How to diagnose and fix it

  1. Verify the battery voltage and charging system output to rule out low voltage or spikes
  2. Inspect the ignition switch connector and wiring for corrosion, loose pins, or chafing
  3. Use a digital multimeter to measure voltage on the run/start sense circuit at the PCM and compare to the service manual specification
  4. Check for aftermarket wiring or accessories that may be backfeeding voltage into the circuit
  5. Test the ignition switch with a multimeter for continuity and voltage output in each key position
  6. If the switch is faulty, replace it and clear the code, then verify the circuit operates correctly
  7. If the wiring and switch check out, diagnose the PCM or BCM for internal faults following manufacturer procedures

Why this code often misleads

  • A high voltage on the run/start circuit can be caused by a backfeed from an aftermarket alarm or remote starter, which many technicians overlook during diagnosis.
  • The code may set intermittently due to a loose ground connection at the ignition switch or PCM, so a wiggle test of the harness is essential.
  • P2535 can be triggered by a weak battery that causes voltage spikes during cranking, even if the battery passes a basic load test.
  • Some vehicles use a smart ignition switch with a separate module, and a fault in that module can mimic a switch failure without any mechanical issue.
  • The PCM may set this code if the ignition switch is left in the run position with the engine off for an extended period, causing a voltage drop that the computer interprets as a high condition.

Can I keep driving with P2535?

If the vehicle starts and runs normally, you can drive it to a repair shop, but avoid turning the engine off and on repeatedly until the fault is fixed. If the engine cranks intermittently or stalls, do not drive because you risk being stranded or losing power steering and brakes.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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