P0856 Diagnostic Trouble Code

P0856 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 P0856 diagnostic trouble code may include:

Fuel pressure too low
Rich or lean exhaust
Diminished fuel efficiency
Reduction in engine performance, especially at low RPM levels

Possible Causes :

A faulty oxygen sensor. This will set a code in itself, however, a faulty oxygen sensor does not automatically condemn the sensor. The code just means that the sensor signal was not within specifications. An air leak or any of the above will cause an erroneous signal. There is a multitude of O2 codes relating to O2 performance which gives a clue to the problematic area.
Some aftermarket accessories and performance modifications
Faulty IMRC actuator/sensor

Repair Processes :

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. It should be pretty close to battery voltage (12 volts). If not, then this is the circuit that has the problem. 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 P0856 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 P0856.

Fortunately, P0856 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

P0856 Trouble Code For Specific Cars

P0856 Saleen S7 Ignition/Distributor Engine Speed Input Circuit Range/Performance
P0856 Lancia Ionos Speed Wheel Sensor RF Input Short Circuit To Battery
P0856 Ford Cougar Main Catalyst Efficiency Below Threshold (Bank 1)
P0856 Hyundai Santamo SCP (J1850) Invalid or Missing Data for Displays
P0856 Lada Xray Shift Solenoid C Performance
P0856 Fiat Duna Lamp Park Input Circuit Short To Battery
P0856 Daewoo Magnus Gate Select Position Circuit Intermittent