GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 GMC C Sierra - 2WD 🢒 DTC 🢒 DTC B013A

Circuit Description

The HVAC control module has an AUTO mode algorithm that is designed to detect a failure with the blower system or a failure with the A/C system. The HVAC control module, when in AUTO mode, requests the engine ON when continuous operation of the A/C compressor (not interrupted by the engine shutting off during stops) is required to cool the cabin in warm or hot weather. The failure detection algorithm monitors duct temperatures while the engine is requested ON under such conditions. If the algorithm does not see duct temperatures become cooler than 120 counts within 30 minutes of requesting the engine on for A/C operation the B013A will set and the HVAC control module will not request engine ON for A/C in warm or hot weather until the B013A is cleared.

The failure detection algorithm will activate if the following conditions are present:

    • The HVAC module is in AUTO mode.
    • The Outside air temperature sensor is in normal operating range.
    • The Inside air temperature sensor is in normal operating range.
    • The Sunload sensor is in normal operating range.
    • The Duct temperature sensors are in normal operating range and are reading warmer than 120 counts (warmer temperatures correspond to lower A/D count values).
    • A temperature setting that requires A/C operation under the current ambient conditions must be selected on the HVAC module.

Algorithm is a word that describes one of the many functions of the software inside the module. The algorithm looks at specific information that the HVAC module receives and based off that information the algorithm outputs specific functions. There is no single circuit or component that performs these functions; it is a combination of inputs, outputs and module function.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B013A A/C System Performance

Conditions for Running the DTC
    • The ignition is turned ON.
    • The HVAC control module is in AUTO mode.
    • The HVAC control module must be requesting engine ON for A/C.

Conditions for Setting the DTC

The HVAC control module is requesting engine ON for A/C and detects duct temperatures warmer than 120 counts for more than 30 minutes.

Action Taken When the DTC Sets
    • The HVAC control module will no longer request the engine on for A/C.
    • No other fail soft actions are taken, and no telltales or other indications are given to indicate a system fault.
    • The DTC will be set until cleared with a scan tool.

Conditions for Clearing the DTC

The DTC can be cleared with a scan tool.

Diagnostic Aids

If the vehicle is under extreme load-such as extended idles at hot ambient or an intermittent failure with the blower system or A/C system This may cause the DTC to set if the failure has been present for more than 30 minutes on one ignition cycle.

Test Description

The number below refers to the step number on the diagnostic table.

  1. This step determines the diagnostic that must be followed to pinpoint the failure.

Step

Action

Yes

No

1

Did you perform the Diagnostic System Check - HVAC Automatic?

Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Automatic

2
  1. Install a scan tool.
  2. Turn ON the ignition.

Is B013A set?

Go to Step 3

Go to Diagnostic Aids

3

Does the blower motor and A/C system operate properly?

Go to Step 4

Go to Too Hot in Vehicle

4
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within Conditions for Running and Conditions for Setting the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

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