P2521
A/C Request A Circuit High
The A/C request input A reads stuck high — typically a short to battery voltage. The ECM cannot pull the line low to read switch state, so the A/C compressor request is treated as invalid and the clutch stays disengaged.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Request wire shorted to battery voltageCommon
- Connector pins corroded - high contact resistanceLess likely
- Supply wire pinched against B+ sourceLess likely
Parts involved
- AC Request Input A
P2521 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.