C1203 Diagnostic Trouble Code

C1203 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 C1203 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
The light may stay on or light intermittently as the DPF regenerates. The engine will be sluggish on acceleration.

Possible Causes :

An air leak forward of the DPF will change the sensor readings resulting in the code
Rusty exhaust systems, cracked exhaust manifolds or damaged or missing gaskets or donuts will cause air leaks.
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. Oxygen sensors signal the engine management computer the amount of oxygen present in the exhaust, which is used in determining and controlling the fuel ratio.

Process Tips

Diagnostic trouble code C1203 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 C1203.

Fortunately, C1203 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

C1203 Trouble Code For Specific Cars

C1203 Mazda 1400 Transmission Transfer Case Contact Plate 'A' Short Circuit To Ground
C1203 Toyota Sa Park Switch Indicates Park with Vehicle Moving
C1203 Cadillac Calais Data Output Link Circuit Failure
C1203 Fiat 505 Lamp Backup Switch Input Circuit Failure
C1203 Moretti Fiat Blower (Fan) Circuit Short to Vbatt
C1203 Mitsubishi Grandis Autolamp On Circuit Failure
C1203 Jensen Ff Seat Driver Recline Forward Switch Circuit Short To Battery