Reduction Agent Pressure Low
The engine control module detects low pressure in the reduction agent (DEF) system.
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What it means (plain English)
The engine’s computer is noticing that the pressure in the diesel exhaust fluid (DEF) system is lower than it should be, which could mean there's a leak or problem with pumps or sensors.
What the computer is actually seeing
The ECM monitors DEF pressure via a pressure sensor; if the signal is below expected values for a certain duration, this code is triggered.
What a healthy reading looks like
Expected DEF pressure is typically around 5-15 psi during operation.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Check the DEF fluid level; it should be above minimum. If it's low, fill it and clear the code. Decision: Clear code and monitor.
- 22. Inspect all DEF lines and connections for leaks or damage. If found, repair or replace the affected components. Decision: Recheck code after repairs.
- 33. Test the DEF pressure sensor. Use a multimeter to check if the sensor voltage is within the expected range, typically 0.5V to 4.5V based on pressure. Decision: If out of range, replace the sensor.
- 44. Check the operation of the DEF pump by observing if it cycles on when key is ON. If not, replace the pump.
Common causes
- Leaking hoses or fittings in the DEF system
- Defective DEF pressure sensor
- Faulty DEF pump
- Contaminated DEF fluid
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's generally safe, but emissions performance may be affected, and you could risk further damage to the system.
Will this code come back after clearing?
If the underlying issue isn't fixed, the code is likely to return.
Why does this code sometimes pair with other DEF codes?
DEF system issues often involve multiple components; a fault in one part can affect others, leading to related codes.
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