P21CA00 fault code and what it can mean
P21CA00 doesn't have one meaning we can give you without reading your vehicle, and it keeps coming back because the fault behind it hasn't been found. We read the full fault description from the ECU at your home, yard or depot and tell you what it's actually pointing at.
Why P21CA00 comes back after clearing
The extra 00 is a sub-code, so P21CA00 is the same fault as P21CA. Its wording isn't one we can confirm from the generic code lists, so on an Audi or any other make, the description from the car's own software is the one to trust.
Whatever it relates to, clearing the code doesn't repair anything. The ECU repeats its check, finds the same problem and stores P21CA00 again, which is why reading it properly beats resetting it.
The usual causes behind P21CA00
| Cause | How it's checked |
|---|---|
| The fault described in the manufacturer's own wording | Full code text read with diagnostic software that covers the make |
| A related fault stored alongside it | Every stored and pending code read together |
| Wiring or connector problems on the system involved | Circuit checks once the system is identified |
Symptoms
- An engine management light that returns after clearing
- Other codes stored at the same time
- Symptoms that depend on the system involved, from none at all to reduced power
Using the vehicle with P21CA00 showing
Until the code's meaning is read from your vehicle, nobody can say for certain how urgent it is. If the car feels normal, short-term use is usually reasonable, but get it read soon and stop if power drops or other warnings appear.
Vans and fleets with P21CA00
If more than one vehicle on your fleet is showing it, we can read them all at your yard or depot in one visit. Regular customers can open a trade account through our trade and partners page.
How we stop P21CA00 coming back
Full code read and diagnosis, £100 + VAT
We read the code's full description and every related fault and live reading, then explain what's wrong in plain English. If a garage needs to replace a part, you'll know exactly which one.
Reviews
Related code P11DC
P11DC is a P1 code, so its meaning is set by each manufacturer. On some Vauxhall and Opel models it's listed as a NOx sensor 2 current performance fault (bank 1, sensor 2), part of the AdBlue system, but other makes can use it differently. We read it the same way as P21CA00, with software that shows your vehicle's own description.
Why does P21CA00 come back after it's been cleared?
Clearing doesn't fix the cause, so the ECU's next check finds the same fault and stores the code again.
Can a remap cause P21CA00?
We can only answer that once the code's meaning is read from your vehicle. A carefully set-up remap shouldn't set fault codes of its own.
Can another fault set off P21CA00?
It can be linked to other faults, which is why we read every stored code together rather than looking at one in isolation.
Can you check P21CA00 on our vans at the depot?
Yes. We'll read each vehicle on site and tell you what the code means on each one.
What should I tell you when I book for P21CA00?
The registration, the make and model, the full code including the 00, and any other warnings or symptoms.
Stop P21CA00 coming back
Book a fault check and we'll find out what P21CA00 means on your vehicle, wherever it's parked.
More fault codes explained
Eccles, Manchester M30 0SF