P0255 indicates an intermittent malfunction in the fuel metering control circuit of the injection pump, specifically related to the cam, rotor, or injector synchronization signal. This code typically appears on diesel engines with electronically controlled distributor or rotary injection pumps when the powertrain control module detects an erratic or dropping signal from the fuel quantity actuator or position sensor. The intermittent nature strongly suggests a loose connection, wiring fault, or component beginning to fail rather than a complete system breakdown.
Corroded, chafed, or loose pins in the harness connectors between the injection pump and the control module are the most frequent cause of intermittent signal loss. Vibration and heat cycles often degrade these connections over time.
The solenoid or sensor responsible for regulating fuel quantity within the pump may have an internal intermittent open circuit or sticking mechanism, causing erratic resistance readings.
Excessive mechanical wear inside the distributor-type pump can cause the cam or rotor to move inconsistently, disrupting the correlation between mechanical position and electrical feedback signals.
High resistance or voltage drops in the supply voltage and ground paths to the injection pump control circuit can cause intermittent communication errors and actuator malfunctions.
Although rare, an internal fault in the PCM's driver circuit for the fuel metering control can produce intermittent signal interruptions, but this should only be considered after all wiring and pump components are verified.
Not always. While internal pump failure can cause this code, wiring and connector problems are equally common culprits. A thorough diagnosis of the electrical circuits should be completed before condemning the pump itself.
No. The intermittent nature of the fault can lead to sudden engine stalling or loss of power without warning, which creates a significant safety risk. The vehicle should be inspected and repaired before regular driving resumes.
Usually no. Although the PCM is sometimes incorrectly blamed for this code, actual PCM failure is rare. Most cases are resolved by repairing wiring or replacing the fuel metering actuator or sensor. The PCM should be the last component tested, not the first.
This refers to the internal mechanical components of distributor-type injection pumps. The code sets when the control module detects an intermittent discrepancy between the commanded fuel metering position and the actual mechanical position of the pump's cam or rotor.