P0AC4
Hybrid/EV Powertrain Control Module Requested MIL Illumination
The hybrid powertrain control module has requested MIL illumination via the inter-module bus. Underlying fault is reported separately by the requesting module.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Downstream fault in hybrid systemCommon
- Communication lag - MIL request stalePossible
Parts involved
- Hybrid Powertrain Cm
- Module Communication Bus
P0AC4 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.