P25AF
Coolant Temperature Control Module Requested MIL Illumination
A dedicated coolant-temperature control module (used on engines with electric coolant pumps and electronic thermostats to keep the cylinder head and block at independent setpoints) has requested the ECM to illuminate the MIL because of an emissions-relevant fault on its side. Original fault is in that module.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Internal fault — read the module DTCsCommon
Parts involved
- Coolant Temp Control Module
P25AF 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.