Powertrain, generic · Computer and auxiliary outputs

P0689 ECM/PCM Power Relay Sense Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

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. P0689 means the sense voltage is too low although the relay is commanded on – the contact does not close or has high resistance, the sense line is open or grounded, or a fuse in the load circuit has blown. GM sets it at 5 V or less with more than 9 V supply in 5 of 6 samples at 1 s, lamp after two trips; GM Europe's V6 below 6 V for 1 s and the 2.0 L turbo below 5 V, both without the lamp. GM includes an open sense line here. Starting problems or stalling follow, and on Saab the throttle control, which uses this voltage, may go into limp mode.

Likely causes

Relay contact burnt or not closing, relay faulty
Fuse in the relay load or sense path blown
High resistance or corrosion in relay carrier, connector or wire
Weak battery

Symptoms

  • Check engine light (depending on the maker)
  • Starting problems or no start
  • Engine stalls or stumbles
  • Possibly electronic throttle limp mode

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

P0688P0690P0685P0562P2610

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