OBD-II code · Network
U0691 Lost Communication With Exhaust Pressure Sensor A
The vehicle bus reports loss of communication with smart exhaust pressure sensor A (typically pre-DPF or pre-turbine). Pressure-based diagnostics switch to a model-based estimate.
Is it safe to drive with U0691?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyBus wiring open or shorted
- PossibleModule without power or ground
- PossibleModule failed
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.5–2 h
- Emissions test
- Likely to fail
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Exhaust Pressure Sensor A, Vehicle Bus Wiring
Related codes
- U0692Lost Communication With Exhaust Pressure Sensor B
- U069FLost Communication With Exhaust Pressure Sensor C
- U068ELost Communication With EGR Temperature Sensor B
- U068FLost Communication With EGR Temperature Sensor C
- U0690Lost Communication With EGR Temperature Sensor D
- U0693Lost Communication With Humidity Sensor
- U0694Lost Communication With Hybrid/EV Battery Pack Coolant Pump A
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.