P21C4
Reductant Heater Relay Control Circuit High
P21C4 is an OBD-II diagnostic trouble code meaning: Reductant Heater Relay Control Circuit High. Common causes: short circuit to positive in the relay control circuit, reagent heater relay malfunction. Estimated repair cost: $17–89.
Symptoms
- Check Engine Light Is On
- Possible reduction in engine power
- Increased NOx emissions
- SCR error message on dashboard
- Problems starting in cold weather
Causes
- Short circuit to positive in the relay control circuit
- Reagent heater relay malfunction
- Wiring harness damage
- Problems with the engine control unit
- Corrosion of contacts or connectors
How to Fix
- Check relay control circuit for short circuit
- Test the reagent heater relay
- Inspect the wiring harness for damage
- Check contacts and connectors for corrosion
- If necessary, replace the relay or repair the wiring
Related codes
Error P21C4 by Vehicle Brand
FAQ
What does the P21C4 code mean?
P21C4 is an OBD-II diagnostic trouble code that indicates: Reductant Heater Relay Control Circuit High
What causes a P21C4 error code?
The most common causes of P21C4 include: Short circuit to positive in the relay control circuit; Reagent heater relay malfunction; Wiring harness damage; Problems with the engine control unit.
How do I fix a P21C4 diagnostic trouble code?
To fix P21C4: Check relay control circuit for short circuit. Test the reagent heater relay. Inspect the wiring harness for damage. For a complete diagnosis, use an OBD-II scanner.
Is it safe to drive with P21C4?
Yes, but get it checked soon
How much does it cost to fix P21C4?
The estimated repair cost for P21C4 is $17–89. Actual cost depends on your vehicle, location, and labor rates.
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