P2534: Ignition Switch On/Start Position Circuit Low

P2534 is the most widely documented of this group. GM's 2025 tables let the TCM fail it when its run/crank input is false while the ECM reports run/crank active, 99 failures out of 240 samples at 25 ms, Type A; the brake control module (EBCM) sets it when its primary wakeup line reads low for 3 s while the network says run or crank, Type B. On the 2016 Volt the line must drop below 2.0 V for 2.5 s. GM bulletins name an ECM harness rubbed through where it passes the left upper control arm bracket on 2020–2025 Silverado/Sierra 2500HD/3500HD (24-NA-124: MIL, stall, no start) and a TCM recalibration for 2008 CTS/STS with the 6L50 (PIP4276B). Ram's 08-037-21 lists it for the 2021 eTorque 1500. Ford's 2014 BOSS 302S table carries it without the M marker.

Medium severity. Can I keep driving?Drive as little as possible. If you feel jerking or the light flashes, stop: a misfire can damage the catalytic converter.

Symptoms

MIL on
Stall or no start
Transmission or other modules set follow-up codes

Most likely causes

Engine harness chafed at a bracket (GM HD trucks, upper control arm bracket)
Run/crank relay or fuse open
Module software needing an update (GM 6L50 TCM, Ram eTorque HCP)
Loose terminal on the wakeup line at TCM or BCM

What to check, in order

Start with the simplest. You can tick off each step.

Check the connector and wiring of the coil indicated
With the connector unplugged, check whether the signal wire is making contact with ground.
Check the condition of the spark plug
Swap the coil with another cylinder and see if the code changes
Measure the power supply and control signal using the manufacturer's wiring diagram

Good to know

Repair difficulty: medium
It can trigger limp mode.
It affects emissions.

What each character of P2534 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
5: Speed and idle
34: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2534?

Drive as little as possible. If you feel jerking or the light flashes, stop: a misfire can damage the catalytic converter.

What causes code P2534?

The most common causes are: engine harness chafed at a bracket (GM HD trucks, upper control arm bracket); run/crank relay or fuse open; module software needing an update (GM 6L50 TCM, Ram eTorque HCP).

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.