P204B code meaning
Reductant Pressure Sensor Circuit Range/Performance
Powertrain system Generic code P20xx codes Check engine light
What P204B means
P204B is a plausibility test: the DEF pressure sensor is electrically fine, but its value disagrees with the system state. GM uses moments when the true pressure is known. The 6.6 L LML sets it if more than 50 kPa appears while the line is empty and unpressurised (Type A, Type B on the 2014 Cruze diesel); GM's 2018 diesel table compares the reading with ambient after the end-of-trip purge, and GM's 2025 DEF controller fails it when the value strays more than 36.4 kPa from ambient before priming. Deutz marks the case on the EMR L1 with failure type 64. Hino released new DCU software in 2016 (SB-16-015) because the unit stored P204B falsely on conventional trucks. A genuine offset mostly means an ageing sensor in the pump module.
P204B at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P204B
- MIL on, possibly only after a second trip
- Emission service message
- Often no noticeable driveability change
Common causes of P204B
- Most likelyPressure sensor offset drift inside the pump module
- PossibleDosing control unit software misjudging the reading (Hino SB-16-015)
- PossibleLine not emptied at shutdown, e.g. afterrun interrupted or frozen DEF
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant pressure sensor
What each part of P204B means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 0 | Area: fuel and air metering and auxiliary emission controls. |
| 4B | The exact fault in that area. |
What to do next
- Note P204B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P204B
What does P204B mean?
P204B means "Reductant Pressure Sensor Circuit Range/Performance". P204B is a plausibility test: the DEF pressure sensor is electrically fine, but its value disagrees with the system state. It is a generic code, so it means the same on every make.
Is it safe to drive with P204B?
Drive gently and only to a workshop. With P204B the car can go into limp mode (reduced power) to protect itself.
Will P204B fail an emissions test?
Yes, it can. P204B is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P204B to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P204B clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.