P2520
A/C Request A Circuit Low
The A/C compressor request input A reads stuck low — typically a short to ground or a permanently asserted request. The ECM either sees A/C demanded all the time (cannot release idle-up, raises fuel use) or cannot distinguish a real request from the stuck low level.
- 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 groundCommon
- Connector pins corroded - high contact resistanceLess likely
- Harness chafing through insulationLess likely
Parts involved
- AC Request Input A
P2520 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.