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First hit on Google: P1ac0 - Starter/Generator Control Module Output Circuit - OBDII Engine Light Trouble Code | AutoCodes.com

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P1AC0 - Starter/Generator Control Module Output Circuit

Repair Importance Level: 3/3

Repair Difficulty Level: 3/3



Possible causes

Faulty Starter/Generator Control Module Cooling Fan Relay

Starter/Generator Control Module Cooling Fan Relay harness is open or shorted

Starter/Generator Control Module Cooling Fan Relay circuit poor electrical connection

What does this mean?

Possible symptoms

Engine Light ON (or Service Engine Soon Warning Light)

P1ac0 Description

The Starter/Generator Control Module (SGCM) coolant pump/fan relay supplies battery voltage to the SGCM coolant pump relay and the SGCM coolant fan relay. The SGCM monitors the temperature of the low side driver for the SGCM coolant pump/fan relay. The temperature sensor of the driver is not serviceable and the data for this sensor is not available on the scan tool. This internal driver temperature sensor aids in detecting a control circuit shorted to ground or a shorted relay coil.

 

The pre-collision system error is likely not related directly to the above. It looks like you have 2 separate problems.

However, they could be related if it's a wiring harness that is damaged or faulty.

 

See below.

The information on that page applies only to certain vehicles made by General Motors. Diagnostic trouble code (DTC) P1AC0, like all DTCs that begin with P1, B1, B2, C1, or C2, and some that begin with P3 or U3, is defined in the SAE J2012 standard as a manufacturer controlled DTC, so each automaker can define what it means for their vehicles. (If John Cleese were making cars, it might be DTC P1AC0, Hovercraft Is Full of Eels.)

For the fourth-generation Prius, we need to look in the Repair Manual (more info) published by Toyota, where it’s P1AC0 (P1AC000), Hybrid/EV Battery Cell Low Voltage. The detection condition is “Voltage difference between battery blocks is larger than the specified value due to an internal malfunction of the HV battery,” and the possible trouble areas include the battery voltage sensor, HV battery, and hybrid battery terminal block. I’d start by checking the battery air intake vent and air filter under the rear seat; the location is shown on page 83 of the Owner’s Manual (PDF). If that’s OK, then use the step-by-step troubleshooting procedure in the Repair Manual.

I wouldn’t make that assumption just yet. When the hybrid vehicle control ECU detected the malfunction reported by DTC P1AC0, it may also have informed the driving support ECU assembly, which would then have stored DTC C1A63, Other System Malfunction, and displayed the “Pre-Collision System Malfunction” message. This wouldn’t indicate a unique problem, just that one computer received a trouble report from another.

It’s possible that there is another problem, of course. To find out for sure, I’d suggest using the Health Check feature of a Toyota Techstream (Global Techstream, GTS) diagnostic system to retrieve the DTCs stored in the driving support ECU assembly. If the car was scanned using a third-party tool, it may not have been able to communicate with this ECU.

 

The nominal specifications for the Ni-MH battery are the same for second-, third-, and fourth-generation Prius cars (168 cells in 28 modules, 201.6 V, 6.5 A·h). I can’t recommend substitutions across generations, however, since we don’t know what other changes Toyota might have made to the battery or cell design.

I’d suggest doing the Repair Manual diagnostic procedure for P1AC0 first, in case the problem isn’t in the HV battery, and if necessary, installing a new HV battery purchased from a Toyota dealer.