What Does P0256 Mean?
The ECM has detected an intermittent malfunction in the injection pump fuel metering control 'A' circuit related to the cam, rotor, or injector mechanism. This indicates the diesel injection pump is sporadically losing proper fuel metering control, causing inconsistent fuel delivery. The intermittent nature suggests a connection or component that fails under certain conditions such as temperature or vibration.
Common Causes
35%
Loose or corroded wiring connector at the injection pump fuel metering solenoid
30%
Failing fuel metering control solenoid with intermittent internal open circuit
20%
Damaged or chafed wiring harness between ECM and injection pump
15%
ECM driver circuit degradation causing intermittent signal loss
Diagnostic Steps
1
Step 1: Wiggle-test the wiring harness and connector at the injection pump fuel metering solenoid while monitoring live PID data for signal dropout — look for any intermittent loss of commanded vs actual fuel metering values.
2
Step 2: Inspect the fuel metering control solenoid connector for corrosion, backed-out pins, or moisture intrusion. Clean with electrical contact cleaner and verify pin tension.
3
Step 3: Measure the fuel metering solenoid resistance with a DVOM — typical spec is 2-8 ohms depending on application. Gently tap the solenoid body while measuring to check for intermittent opens.
4
Step 4: Perform a voltage drop test on both the power supply and ground circuits to the metering solenoid while cranking and running — voltage drop should be less than 0.5V on each side.
5
Step 5: If wiring and solenoid test good, monitor ECM driver output with an oscilloscope to verify consistent PWM signal to the metering valve during operation.
Estimated Repair Cost
$200 - $1,200
Parts + labor, varies by vehicle and location
The ECM has detected an intermittent malfunction in the injection pump fuel metering control 'A' circuit related to the cam, rotor, or injector mechanism. This indicates the diesel injection pump is sporadically losing proper fuel metering control, causing inconsistent fuel delivery. The intermitten...
The most common cause of P0256 (Injection Pump Fuel Metering Control "A" Intermittent (Cam/Rotor/Injector)) is: Loose or corroded wiring connector at the injection pump fuel metering solenoid
Typical repair costs for P0256 range from $200 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is generally drivable but may experience intermittent power loss, rough running, or stalling. Repair within one week to prevent potential no-start conditions.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0256 to identify the root cause.
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Quick Info
Category
Powertrain
System
Diesel Fuel Injection System
Difficulty
Type
Generic (SAE)
Recommended Tools
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