P0408 Diagnostic Trouble Code

P0408 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 P0408 diagnostic trouble code may include:

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
Faulty or damaged wiring
Hesitation upon acceleration
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)
Defective ECU strategies or components will prevent proper regeneration

Repair Processes :

Now, clear the codes and test-drive the vehicle to see if the code is reset. With the valve disconnected, the red voltmeter lead should be attached to the IMRC valve power wire and the black voltmeter lead connected to ground. 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.

Process Tips

Diagnostic trouble code P0408 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 P0408.

Fortunately, P0408 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

P0408 Trouble Code For Specific Cars

P0408 Mazda Ms-9 (CAN) Lack of Acknowledgement From Engine Management
P0408 Volkswagen New Beetle Right Rear Sensor Circuit Failure
P0408 Mitsubishi Celeste Audio Rear Control Unit is Not Responding
P0408 Rover City Rover Ignition Coil H Primary/Secondary Circuit Malfunction
P0408 Fiat 25 Lamp ABS Warning Output Circuit Short To Battery
P0408 American Traveler Air Suspension LF Air Spring Solenoid Output Circuit Open
P0408 Ginetta G10 Oil Level Switch Circuit Failure