P204F: Reductant System Performance (Bank 1)

P204F (Bank 1) is the functional check of the whole DEF delivery path: the parts are electrically intact, yet the system cannot build or hold the pressure needed for dosing. GM's 6.6 L LML stores a Type A code if the pump module stays at or below 350 kPa after 30 build-up and venting attempts of at least 10 s each; the 2014 Cruze diesel uses 375 kPa and 20 attempts. GM treats P204F as a tamper fault. On Hino trucks P204F is the engine ECU's summary code for urea SCR faults seen by the dosing unit; per TT-14-025 it clears only after the DCU faults are repaired and the SCR memory has been reset. Ram's 3.0 L V6 EcoDiesel received PCM updates covering it (18-008-21). CARB demands this delivery check. Causes include frozen or clogged lines, a worn pump, air leaks or an empty tank.

Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.

Symptoms

• MIL and DEF warning on
• Countdown to speed or power limitation
• Code returns after clearing until the cause is fixed

Most likely causes

• DEF line clogged by crystals or frozen
• Worn DEF pump that cannot reach target pressure
• Air leak on the suction side or loose line couplings
• Dosing unit faults repaired but SCR memory not reset (Hino)
• Control module software needing an update (Ram 3.0 L)

What to check, in order

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

1. Check the AdBlue/DEF level and quality, and do not add additives or water
2. Compare the reading with other engine data while varying the engine speed.
3. Look for white crystals around the injector and the tank
4. Check connectors and heaters with the scanner
5. Run the dosing test available on your diagnostic tool
6. Replace parts only when the test points to that component

Good to know

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

What each character of P204F means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 0: Subsystem depends on the code range
• 4F: Specific fault in that system

Frequently asked questions

Can I keep driving with code P204F?

You can drive in moderation to get to a repair shop, because the engine usually runs well. Watch the instrument cluster: if a countdown appears, get it repaired before the car stops starting.

What causes code P204F?

The most common causes are: dEF line clogged by crystals or frozen; worn DEF pump that cannot reach target pressure; air leak on the suction side or loose line couplings.

Related codes

• P205FReductant System Performance (Bank 2)
• P20E8Reductant Pressure Too Low
• P20E9Reductant Pressure Too High
• P202EReductant Injection Valve Circuit Range/Performance (Bank 1 Unit 1)
• P208BReductant Pump A Control Performance/Stuck Off
• P218FReductant No Flow Detected

Sources

• gsi.ext.gm.com: 14OBDG10 Engine Diagnostics
• gsi.ext.gm.com: 14OBDG04 Engine Diagnostics
• static.nhtsa.gov: MC 10117725 9999
• static.nhtsa.gov: MC 10220589 9999

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.