C3691 Diagnostic Trouble Code

C3691 is a kind of OBD-II Diagnostic C-Chassis Diagnostic Trouble Code.

It is considered generic because it applies to all makes and models of vehicles, although specific repair steps may be different depending on your car model.

Symptoms

Symptoms of a C3691 diagnostic trouble code may include:

Faulty or damaged wiring
The engine oil will exhibit dilution from the ECUs attempts to increase engine temperature. Some vehicles advance the fuel injection timing slightly after top center to afterburn a small amount of fuel to increase exhaust temperatures. Some of this fuel enters the crankcase. When the ECU determines the necessity to regenerate the DPF, the service life of the oil be shortened significantly
Poor fuel economy
If the DPF is not cleared the ECU will revert to the "Limp Home Mode" until the situation is corrected

Possible Causes :

A large air leak at or near the number one oxygen sensor would also cause a lean mixture.
Faulty IMRC actuator relay (if equipped)
A large vacuum leak would cause a massive amount of un-metered air to enter the intake manifold resulting in an overly lean mixture.

Repair Processes :

If all testing has passed so far yet you still have the same code, check your scan tool and see if it can open and close the IMRC valve. Look for missing ground strap or a rusty ground where the fuel tank is grounded to the frame. Check for damage to the wiring harness connector. Replace the oxygen sensor that is downstream from the catalytic converter on the side of the engine that does not contain cylinder #1. Also, if a oxygen sensor code stating "heater circuit malfunction" the sensor has most probably failed.

Process Tips

Diagnostic trouble code C3691 is not difficult to diagnose and repair. Thus, it always pays to have a qualified technician to look after your vehicle should this error code arise.

Diagnosing this code requires the engine to be in good running shape, without unmetered air entering the engine. If other codes that relates to misfiring condition, lean running or air entering the engine is present, then you must first fix those error codes before C3691.

Fortunately, C3691 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

C3691 Trouble Code For Specific Cars

C3691 Puma Gte Fuel Temperature Sensor #2 Circuit Failure
C3691 Honda Pilot Rear Cargo Door Unlock Circuit Open
C3691 Simca Horizon Interior Fan Control Circuit Short to Ground
C3691 Subaru Rex License Lamp Circuit Short to Battery
C3691 Batten 3.6 B Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)
C3691 Mitsubishi Gaus Autolamp Delay Increase Circuit Short To Ground
C3691 Crossley Shelsley Fuel Tank Pressure Sensor Circuit Failure