What does it mean?
P1691 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Reductant Injection Valve Circuit High - Positive Side .
Symptoms
- MIL on together with an exhaust fluid system warning and a countdown message
- Engine power reduction and eventually a no-restart condition once the warnings expire
- Nitrogen oxide related codes stored alongside this one
- Exhaust fluid consumption stops, with the tank level no longer falling
- White crusty deposits visible around the dosing valve and its mounting
- Vehicle speed limited on some designs
Likely causes
- Open circuit on the positive supply wire to the reductant dosing valve
- Short to battery positive on the dosing valve circuit
- Disconnected or corroded dosing valve connector, which sits in a hot and salt-exposed area
- Crystallised urea deposits around the valve damaging the seals and the connector
- Dosing valve with an open internal winding
- Blown fuse or failed relay feeding the reductant control circuit
- Failed output driver in the reductant control module
How to fix it
- Inspect the dosing valve connector for urea crystals, corrosion and heat damage before any other test
- Measure the valve winding resistance and compare it with the specification
- Check the supply fuse and relay, and confirm battery voltage reaches the valve connector with the ignition on
- Test the circuit for an open or a short to battery positive with the module unplugged
- Command the dosing valve with the scan tool and watch the current draw and the system pressure response
- Clean crystallised deposits from the valve and its seat and renew the seals
- Replace the dosing valve if it is electrically open or blocked, and repair the harness section if it is damaged