P268C: Cylinder 1 Injector Data Incompatible

Every modern diesel injector carries a correction code from the factory flow test, and the controller must hold the code of the injector in cylinder 1. P268C sets when that code is missing, outside its range or fails the checksum. GM's 2014 four-cylinder diesel table (14OBDG04) checks the injector quantity adjustment (IQA) checksum once per drive cycle before driving, Type B. Later GM V8, six- and four-cylinder diesel tables rate it Type A, set if the code at DID $60 was never written. Ford's 2023 diesel summary (6.7 L and 3.0 L) runs the check continuously within about 0.5 s. Cylinder 1 exists on every engine, so this is the most widely used code of the series.

Cylinder 1 is numbered according to the manufacturer: check your engine's manual before working on it.

Symptoms

• Check engine light on
• Uneven running or knock from cylinder 1

Most likely causes

• Correction code of a new cylinder 1 injector not entered
• Code entered with a typing error, so the checksum fails
• Controller replaced without transferring injector codes

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the connector and wiring of the injector indicated
2. Measure the resistance and compare it with the manufacturer's specification
3. Check the control signal with an oscilloscope; on direct injection or diesel engines, leave this to a repair shop because of the high voltages
4. On diesels, check the per-cylinder injection corrections

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P268C means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 6: Control modules and outputs
• 8C: Specific fault in that system

Frequently asked questions

Can I keep driving with code P268C?

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 P268C?

The most common causes are: correction code of a new cylinder 1 injector not entered; code entered with a typing error, so the checksum fails; controller replaced without transferring injector codes.

Related codes

• P268DCylinder 2 Injector Data Incompatible
• P2696Injector Data Incompatible
• P268AFuel Injector Calibration Not Learned/Programmed
• P0201Cylinder 1 Injector A Circuit/Open
• P02EECylinder 1 Injector Circuit Range/Performance

Sources

• law.cornell.edu: 13 CCR 1968.2
• gsi.ext.gm.com: 14OBDG04 Engine Diagnostics
• gsi.ext.gm.com: 18OBDG04 Engine Diagnostics
• 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.