P0AC4: Hybrid/EV Powertrain Control Module Requested Malfunction Indicator Lamp Illumination
What to do
As with P0700 and P0A7B: this is a message, not a fault. Ask for the codes stored in the hybrid control module itself — a scan of the engine module alone shows only this request.
What this code means
The hybrid powertrain control module has asked the engine module for the warning lamp — the third arrival of the corpus's request-record pattern in this block, after P0700's transmission original and P0A7B's battery version.
This code names no fault. It records that the hybrid system's coordinating module has something to report, and the code describing what is stored in that module, where a basic reader talking only to the engine module cannot see it. The same trap and the same defence as its siblings: on a hybrid, an unexplained request code invites the most expensive guess available, and reading the requesting module's own memory replaces the guess with an address.
Likely causes
Start here
Less common
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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