P204F on GMC
Reductant System Incorrect Quantity
P204F on GMC vehicles indicates reductant system incorrect quantity. Au7o has documented this code across 1 GMC model — most commonly on Canyon. This code is set on diesel SCR-equipped vehicles when the reductant (diesel exhaust fluid / DEF) system delivers an incorrect quantity of DEF, meaning the actual dosing or pressure doesn't match what the computer commanded. The reductant system pumps and injects DEF into the exhaust so the SCR catalyst can break down NOx emissions, and the computer monitors pressure and dosing performance. When it sees too much or too little fluid being delivered, or pressure that's out of range, it flags this performance code. Typical roots are a clogged or failing DEF pump, contaminated fluid, a faulty pressure sensor, or a bad injector. Typical repair costs on GMC range from $200 to $3,500, depending on the specific model and root cause.
Common Causes of P204F
- •Contaminated or poor-quality diesel exhaust fluid (DEF)
- •Faulty reductant (DEF) pressure sensor
- •Clogged DEF pump filter or weak/failing DEF pump
- •Faulty or clogged reductant injector
- •Leaking, cracked, or loose DEF lines/clamps
- •Crystallized DEF buildup blocking the system
- •Failed reductant/SCR control module
- •Wiring or connector faults in the reductant system
P204F on GMC by Model
GMC Canyon(1 issue)
- 2.8L Duramax DEF System Faults and DPF Regeneration Issues2016-2025
The 2016+ Canyon Duramax 2.8L LWN diesel uses DEF (Diesel Exhaust Fluid) injection and a DPF (Diesel Particulate Filter) as part of its SCR emissions system. Owners frequently report DEF quality/level sensor faults, DPF regeneration failures in stop-and-go use, DEF pump failures, and NOx sensor faults. Trucks used primarily for short trips often cannot complete DPF regeneration cycles, leading to DPF plugging and the truck going into reduced power mode. GM issued multiple TSBs on DEF sensor calibration and DPF regen procedures.
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View P204F across all makes →Frequently Asked Questions
What does P204F mean on GMC?▼
P204F stands for "Reductant System Incorrect Quantity." This code is set on diesel SCR-equipped vehicles when the reductant (diesel exhaust fluid / DEF) system delivers an incorrect quantity of DEF, meaning the actual dosing or pressure doesn't match what the computer commanded. The reductant system pumps and injects DEF into the exhaust so the SCR catalyst can break down NOx emissions, and the computer monitors pressure and dosing performance. When it sees too much or too little fluid being delivered, or pressure that's out of range, it flags this performance code. Typical roots are a clogged or failing DEF pump, contaminated fluid, a faulty pressure sensor, or a bad injector. On GMC specifically, this code is documented across 1 model.
What causes P204F on GMC vehicles?▼
Common causes on GMC: Contaminated or poor-quality diesel exhaust fluid (DEF), Faulty reductant (DEF) pressure sensor, Clogged DEF pump filter or weak/failing DEF pump, Faulty or clogged reductant injector, Leaking, cracked, or loose DEF lines/clamps. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P204F on a GMC?▼
Repair costs on GMC range from $200 to $3,500, depending on the specific model and root cause.
Which GMC models have P204F documented?▼
Au7o has documented P204F on 1 GMC model: Canyon.