P2691 refers to the injector in cylinder 6. For six-cylinder diesels it is the last of the per-cylinder codes: GM's 2025 table 25OBDG04B stops at P2691, while the V8 table 25OBDG04A goes on to P2693. In both 2025 tables the check is always active on production controllers and fails if the end-of-line adjustment value was never written; as a further guard, a separate plausibility test under P060C looks at the size of the computed adjustment values. GM rates P2691 Type A. Ford's 2023 diesel summary lists it for its 3.0 L and 6.7 L engines. Programming the code printed on the cylinder 6 injector normally clears it; a recurring fault after correct entry points to the controller.
Medium severity. Can I keep driving?Drive as little as possible and go to a repair shop. If you smell fuel or the engine is shaking badly, do not keep driving.
Cylinder 6 is numbered according to the manufacturer: check your engine's manual before working on it.
Symptoms
- Check engine light on
- Possible knock or smoke from the affected cylinder
Most likely causes
- Cylinder 6 injector code missing after replacement
- Entered value rejected as implausible by the software
- Controller memory fault losing stored injector data
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P2691 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 6: Control modules and outputs
- 91: Specific fault in that system
Frequently asked questions
Can I keep driving with code P2691?
Drive as little as possible and go to a repair shop. If you smell fuel or the engine is shaking badly, do not keep driving.
What causes code P2691?
The most common causes are: cylinder 6 injector code missing after replacement; entered value rejected as implausible by the software; controller memory fault losing stored injector data.
Related codes
- P2690Cylinder 5 Injector Data Incompatible
- P2692Cylinder 7 Injector Data Incompatible
- P2696Injector Data Incompatible
- P0206Cylinder 6 Injector A Circuit/Open
- P02F3Cylinder 6 Injector Circuit Range/Performance
- P060CInternal Control Module Main Processor Performance
Sources
- law.cornell.edu: 13 CCR 1968.2
- gsi.ext.gm.com: 25OBDG04B
- gsi.ext.gm.com: 25OBDG04A
- fordservicecontent.com: obd summary diesel 2023
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.