C0691 Diagnostic Trouble Code

C0691 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 C0691 diagnostic trouble code may include:

Malfunction Indicator Lamp (MIL) illuminated
Carbon Buildup on O2 Sensor
Poor fuel economy
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

Possible Causes :

A large vacuum leak would cause a massive amount of un-metered air to enter the intake manifold resulting in an overly lean mixture.
Faulty IMRC actuator/sensor
Low fuel pressure caused by a clogged filter, failing fuel pump, failed fuel pressure regulator or clogged or leaking injectors.

Repair Processes :

If the engine displays a miss and there wasn't a code, determine which cylinder is misfiring. If the exhaust manifold is visible, spay or pour a small amount of water on each cylinder exhaust port. Water will evaporate immediately on good cylinders and slowly on the missing cylinder. If this can't be accomplished pull the plugs and check the condition. 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. Find out what kind of system you have and verify that voltage to the fuel level sensor is present at the fuel pump wiring harness.

Process Tips

Diagnostic trouble code C0691 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 C0691.

Fortunately, C0691 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

C0691 Trouble Code For Specific Cars

C0691 Vauxhall Viceroy Pressure Control Solenoid Intermittent
C0691 Westfield Xtr SCP (J1850) Invalid or Missing Data for Navigation
C0691 Chenard Walcker 3-litre Door Unlock Disarm Output Circuit Short To Ground
C0691 Volvo Duett
C0691 Shelby Cobra Intake Air Temperature Circuit High Input
C0691 Batten 3.6 B Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)
C0691 Renault 17