P0C91 Diagnostic Trouble Code

P0C91 is a kind of OBD-II Diagnostic P-Powertrain 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 P0C91 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 :

Pack the connector cavity with dielectric silicone compound (same stuff they use for light bulb sockets and spark plug wires) and reassemble. 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. Look at the plug wires to make sure they are not burnt or laying on the exhaust.

Process Tips

Diagnostic trouble code P0C91 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 P0C91.

Fortunately, P0C91 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

P0C91 Trouble Code For Specific Cars

P0C91 Smart Fortwo Lamp Air Bag Warning Indicator Circuit Open
P0C91 Honda Ssm RESCU/VEMS Input Circuit Short to Battery
P0C91 Subaru Xt MAF Ground Malfunction
P0C91 Plymouth Cuda Evaporative Emission Control System Pressure Sensor Malfunction
P0C91 Peugeot Ion
P0C91 Citroen Jumpy Iii Fuel Pump Control Out Of Range
P0C91 Mazda Eunos TRS Circuit Intermittent Malfunction