NOx Absorber Over Temperature
Table of contents
P21B4 RAM Possible Causes
- Exhaust Temperature Sensors failed in-range low
- Unintended fueling
- Damaged NOx absorber catalyst
How do I fix code P21B4 RAM?
Check the “Possible Causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector’s pins.
Cost of diagnosing the P21B4 RAM code
The cost of diagnosing the P21B4 RAM code is 1.0 hour of labor. The auto repair labor rates vary by location, your vehicle’s make and model, and even your engine type. Most auto repairs shops charge between $75 and $150 per hour.
Possible Symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
P21B4 RAM Description
When the engine runs in DeNOx mode, the Powertrain Control Module (PCM) monitors how much post-injection fuel has been injected. Once it exceeds a threshold, the measured O2 Sensor 1/1 is supposed to be lower than a threshold. If after a sufficient amount of post fuel is injected, the O2 Sensor 1/1 value is still high for a calibrated time, the fail counter is incremented by 1. If it is not, it is decremented by 1. If the counter has been incremented or decremented for a calibrated number of times, and the counter value is greater than a calibrated value, this fault is set. The Diagnostic Trouble Code (DTC) will set when the NAC outlet temperature exceeds a calibrated high threshold for a calibrated period of time.