P20CC: Exhaust Aftertreatment Fuel Injector A Control Performance

Unlike the circuit codes, this one judges what the hydrocarbon doser actually does. On the 6.6 L Duramax LML/LGH, GM table 15OBDG09 sets it when the outlet of the oxidation catalyst runs more than 300 °C hotter than its inlet for 180 s although no regeneration is under way and more than 900 s have passed since the last one; that heat can only come from fuel the doser should not be delivering. It is a Type A fault, so the MIL comes on after one trip. To keep the nozzle free, the same GM software pulses it briefly at 100 Hz at set soot levels. CARB requires makers to flag any injection fault that stops the filter from regenerating. Stuck positions have separate codes (P20CF, P20D0).

Symptoms

• Check engine light on
• Unexpectedly high exhaust temperatures, possibly white smoke or fuel smell
• Higher fuel consumption

Most likely causes

• Doser leaking or dribbling fuel into the exhaust while closed
• Coked nozzle tip with distorted spray
• Exhaust temperature sensor before or after the catalyst reading wrong

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. Compare the reading with other engine data while varying the engine speed.
3. Measure the resistance and compare it with the manufacturer's specification
4. Check the control signal with an oscilloscope; on direct injection or diesel engines, leave this to a repair shop because of the high voltages
5. On diesels, check the per-cylinder injection corrections

Good to know

• Repair difficulty: hard
• It can trigger limp mode.
• It affects emissions.

What each character of P20CC means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 0: Subsystem depends on the code range
• CC: Specific fault in that system

Frequently asked questions

Can I keep driving with code P20CC?

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 P20CC?

The most common causes are: doser leaking or dribbling fuel into the exhaust while closed; coked nozzle tip with distorted spray; exhaust temperature sensor before or after the catalyst reading wrong.

Related codes

• P20CBExhaust Aftertreatment Fuel Injector A Control Circuit/Open
• P20CFExhaust Aftertreatment Fuel Injector A Stuck Open
• P20D0Exhaust Aftertreatment Fuel Injector A Stuck Closed
• P20D2Exhaust Aftertreatment Fuel Injector B Control Performance
• P2698Exhaust Aftertreatment Fuel Injector A Performance
• P20E2Exhaust Gas Temperature Sensor 1/2 Correlation (Bank 1)

Sources

• gsi.ext.gm.com: 15OBDG09 Engine Diagnostics
• gsi.ext.gm.com: 16OBDG09 Engine Diagnostics
• law.cornell.edu: 13 CCR 1968.2

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.