Faulty or sticking cylinder 4 fuel injector; Wiring or connector fault in the cylinder 4 injector circuit; Low fuel pressure or fuel supply restriction, such as a blocked filter or weak pump; Incorrect or disturbed mechanical timing, such as a stretched or slipped timing belt or chain or a pump drive issue (engine dependent); Crankshaft or camshaft position sensor signal fault; Outdated or faulty control unit calibration, where the manufacturer has issued a fix for this fault; Internal control unit driver fault.

P01D1

Cylinder 4 Injection Timing Performance - Over Retarded.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
D1: FaultThe specific fault in that area

What it means

P01D1 is a generic powertrain code meaning the actual fuel injection timing on cylinder 4 is later than the engine control unit has commanded, beyond an allowed limit. The control unit compares commanded and measured or inferred injection timing and sets the code when cylinder 4 is over retarded. It is most associated with diesel and direct injection systems, and the exact monitoring method depends on the engine.

Symptoms

Engine management warning light on
Rough running or misfire on one cylinder, especially at idle
Loss of power or poor acceleration
Increased exhaust smoke, particularly white or grey smoke when cold
Hard starting or extended cranking
Diesel knock or uneven combustion noise

Possible causes

Faulty or sticking cylinder 4 fuel injectorlikely
Wiring or connector fault in the cylinder 4 injector circuitlikely
Low fuel pressure or fuel supply restriction, such as a blocked filter or weak pumppossible
Incorrect or disturbed mechanical timing, such as a stretched or slipped timing belt or chain or a pump drive issue (engine dependent)possible
Crankshaft or camshaft position sensor signal faultpossible
Outdated or faulty control unit calibration, where the manufacturer has issued a fix for this faultrare
Internal control unit driver faultrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting engine temperature, load and rpm when the fault set
Check for related codes such as misfire, fuel pressure, rail pressure or position sensor faults and deal with those first
Inspect the cylinder 4 injector wiring and connector, and the engine harness, for chafing, corrosion, oil ingress or poor pin tension
Check fuel level, fuel quality and filter condition, and test fuel supply and rail pressure against specification
View live data for injector correction values or cylinder balance figures and compare cylinder 4 with the others
Check crankshaft and camshaft sensor signals and their wiring, and confirm the sensors are secure and undamaged
Verify mechanical timing against the manufacturer procedure for that engine
Test the cylinder 4 injector electrically and by flow or leak-off checks, following the procedure for the specific engine

How to fix

Repair or replace damaged wiring or connectors in the cylinder 4 injector circuit
Replace the cylinder 4 injector if it is faulty, and code or adapt it to the control unit if the manufacturer requires
Replace the fuel filter and repair any fuel supply or pressure fault found
Correct the mechanical timing and replace worn drive components, such as the belt, chain or tensioner, as required
Replace a faulty crankshaft or camshaft position sensor
Update the control unit calibration only if a known fix exists for this fault

Can I keep driving?

Medium severity

Short, gentle journeys to a workshop are usually acceptable, but avoid heavy loads and high revs. If the engine runs very roughly, knocks loudly or smokes heavily, stop driving, as continued use can damage the engine or catalytic converter or diesel particulate filter.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.