Powertrain, generic (extended)

P25B7 Auxiliary Ignition Switch On/Start Position Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P25B7 covers the hard-wired input from an auxiliary ignition switch that commands the On and Start positions from a second location, for example a rear panel behind the cab, a work platform or a remote station on a chassis-cab truck. The module flags a state on this line it cannot interpret, such as an open circuit, without saying whether the level is too low or too high. No manufacturer documents P25B7 publicly. The nearest published logic is the main run/crank input, for which the GM brake control module in table 25OBDG04A sets P2534 when its wake-up line stays low for 3 s while the ECM reports run or crank. Navistar describes remote start and shutdown panels for PTO bodies built on this principle. For the driver, the remote start point may stop responding while the key in the cab still works.

Likely causes

Open wire or loose connector in the harness to the body or remote panel
Worn or corroded contacts in the auxiliary switch
Faulty or modified upfitter wiring
Input stage of the reading module damaged

Symptoms

  • Engine cannot be started or switched on from the auxiliary position
  • Normal key or push-button start still works
  • Stored code, often without other complaints

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–450
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

auxiliary ignition switchwiring harness

Related codes

P25B8P25B9P2533

References: law.cornell.edu, http:, gsi.ext.gm.com.