Diagnostic article Generic OBD-II
P0A85: Fan control feedback stays high despite a lower command
P0A85 checks high battery-fan control feedback while the commanded level is below its qualifying limit.
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Documented application
2009 General Motors diagnostic parameter file 09OBDG08 Engine Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability established.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
The P0A85 strategy in GM's BAS hybrid table checks fan-control feedback above 95 percent while the fan is on and the command remains below 80 percent. The command qualification is crucial: a high feedback value is not interpreted in isolation.
Compare the requested and returned control levels
A feedback value near full scale can be inappropriate when the controller requested a lower level. The source therefore pairs the returned control feedback with the commanded level. It does not directly classify the fan as physically stuck at a particular speed.
The separate P0A83 stuck-on check uses speed feedback under an off command. Keeping that distinction prevents a control-signal disagreement from being automatically described as continuous fan rotation.
Qualified persistence supports the decision
The energy-storage controller must be in Run or Service with system voltage inside the documented window. The failure counter requires 188 of 250 observations, sampled every 20 milliseconds. A momentary mismatch during a transition is not necessarily the same recorded pattern.
Preserve command, control feedback and speed feedback as separate evidence. Use the applicable vehicle circuit procedure to identify the source of the high returned control signal. Verification should demonstrate that feedback follows the lower commanded level and that monitoring completes. Clearing P0A85 or seeing the fan cool the battery once does not establish that the control-feedback disagreement is corrected.
Source and applicability
2009 General Motors diagnostic parameter file 09OBDG08 Engine Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability established. This explanation describes the documented monitor, not a universal repair procedure.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
Hybrid/EV Battery Pack Cooling Fan 1 Control Circuit High
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT