P0691
System
Powertrain (Cooling)
Scanner required
Enhanced OBD2 scanner (live data graphs, freeze frame, battery voltage test)

Cooling Fan 1 Relay Control Circuit Low

Understand P0691, common causes, and the right TOPDON scanner to diagnose it.

Fan 1 relay control circuit shorted low.

Common symptoms

  • Overheating
  • Fan runs constantly or never

Typical causes

  • Short to ground in fan relay circuit
  • Failed relay
  • ECM driver fault

What scanner do you need?

Enhanced OBD2 scanner (live data graphs, freeze frame, battery voltage test)

Use live data and freeze frame to confirm the fault before replacing parts. ABS, SRS, and network U-codes usually require a full-system scanner.

Diagnostic tips

  • Record freeze frame data when the code first sets
  • Clear the code only after fixing the root cause
  • Check for related pending codes that point to a common issue
  • Verify battery voltage is above 12.4V before chasing sensor codes

Recommended TOPDON scanners

Frequently asked questions

Can I diagnose P0691 with a basic code reader?
P0691 may set in the engine module, but related diagnostics often benefit from an enhanced or full-system scanner with live data and freeze frame.
Is it safe to drive with P0691?
It depends on the code and symptoms. Flashing check engine lights and misfire codes should be addressed immediately. Consult a professional if unsure.