Powertrain, generic · Computer and auxiliary outputs

P0690 ECM/PCM Power Relay Sense Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

The engine module switches its main relay coil to ground (control circuit), reads the switched voltage back on a sense line and keeps the relay on briefly after ignition off to save learned values. P0690 means the sense voltage is too high: voltage is present although the relay has been off for 2 s – a welded or sticking contact, or external voltage fed in through a short – or, on some systems, overvoltage above 18 V with the relay on. GM sets it at 4 V or more with the relay off, in 50 of 63 samples at 100 ms, lamp after two trips; GM Europe's 2.0 L turbo above 2 V with the relay off or above 18 V with it on, for 2 s, and advises fixing other short-to-voltage codes first. Modules, fans or pumps may keep running after switch-off and the battery drains overnight.

Likely causes

Relay contact sticking or welded
Short to voltage on the sense or load line (external feed from another component)
Control wire shorted to ground (relay permanently on)
Overvoltage from the alternator regulator (where the 18 V limit applies)

Symptoms

  • Check engine light
  • Module, fan or pumps keep running after ignition off
  • Battery drains overnight

Repair estimate

DifficultyEasyDIY possible
Parts and labour€10–250
Time0.3–2 h

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

Parts involved

ecm power relayrelay control circuitengine control module

Related codes

P0689P0688P0686P068BP0563

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