Cause
Worn or leaking fuel injectors
A common rail injector holds back fuel at fifteen hundred bar or more with a needle and seat measured in microns. As that seat wears it fails in both directions at once — delivering more than commanded while open, and continuing to pass fuel after it closes — and the engine module sees the sum as excess fuelling on that cylinder.
The leak-back test is the measurement that settles it, and it works by comparison rather than against a specification: with the return lines instrumented, a worn injector returns visibly more fuel than its neighbours. That comparison is also what answers the question that actually decides the repair — whether one injector has failed or the whole set is wearing together. On an engine where the labour to reach them dominates the bill, doing a drifting set in one visit is far cheaper than doing them one at a time.
Check the oil. A leaking injector puts diesel down the cylinder wall into the sump, and an oil level that has risen above maximum on a diesel is a hazard rather than a curiosity — in the worst case the engine runs on its own oil and cannot be switched off.
Typically specialist work. Needs equipment or training most home workshops do not have.
Codes this can cause (33)
Codes where this is a likely explanation first, rather than merely a possible one.
- P01CC Cylinder 1 Injection Timing Performance - Over Advanced Likely for this code Moderate
- P01CE Cylinder 2 Injection Timing Performance - Over Advanced Likely for this code Moderate
- P01D0 Cylinder 3 Injection Timing Performance - Over Advanced Likely for this code Moderate
- P01D2 Cylinder 4 Injection Timing Performance - Over Advanced Likely for this code Moderate
- P01D4 Cylinder 5 Injection Timing Performance - Over Advanced Likely for this code Moderate
- P01D6 Cylinder 6 Injection Timing Performance - Over Advanced Likely for this code Moderate
- P020A Cylinder 1 Injection Timing Likely for this code Moderate
- P020B Cylinder 2 Injection Timing Likely for this code Moderate
- P020C Cylinder 3 Injection Timing Likely for this code Moderate
- P020D Cylinder 4 Injection Timing Likely for this code Moderate
- P020E Cylinder 5 Injection Timing Likely for this code Moderate
- P020F Cylinder 6 Injection Timing Likely for this code Moderate
- P021A Cylinder 7 Injection Timing Likely for this code Moderate
- P02CC Cylinder 1 Fuel Injector A Offset Learning At Min Limit Likely for this code High
- P02CE Cylinder 2 Fuel Injector A Offset Learning At Min Limit Likely for this code High
- P02D0 Cylinder 3 Fuel Injector A Offset Learning At Min Limit Likely for this code High
- P02D2 Cylinder 4 Fuel Injector A Offset Learning At Min Limit Likely for this code High
- P02D4 Cylinder 5 Fuel Injector A Offset Learning At Min Limit Likely for this code High
- P02D5 Cylinder 5 Fuel Injector A Offset Learning At Max Limit Likely for this code High
- P02D6 Cylinder 6 Fuel Injector A Offset Learning At Min Limit Likely for this code High
- P02D7 Cylinder 6 Fuel Injector A Offset Learning At Max Limit Likely for this code High
- P219A Bank 1 Air-Fuel Ratio Imbalance Likely for this code Moderate
- P219B Bank 2 Air-Fuel Ratio Imbalance Likely for this code Moderate
- P219F Cylinder 4 Air-Fuel Ratio Imbalance Likely for this code Moderate
- P21A0 Cylinder 5 Air-Fuel Ratio Imbalance Likely for this code Moderate
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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