A/C - Does Not Cool/Can't Change Mode/DTC's Set
Bulletin No.: 07-01-38-009BDate: November 28, 2007
TECHNICAL
Subject:
EI07264 - Manual HVAC, Temperature or Mode Actuator Performance, A/C Does Not Cool, Unable to Change Mode, DTC B0228, B0413, B0423, B0433, B3779, B3782 (Diagnose for Intermittent Wiring Connection at RH BEC)
Models:
2007-2008 Chevrolet Silverado
2007-2008 GMC Sierra
Extended and Crew Cab Models Only with Manual Temperature Control HVAC System (RPO C67)
Supercede:
This bulletin is being revised to end the need for engineering information and to provide diagnostic procedures to accurately diagnose this condition. Please discard Corporate Bulletin Number 07-01-38-009A (Section 01 - HVAC).
Condition
This concern only applies to Extended or Crew cab vehicles.
If the customer did not bring their vehicle in for this concern, do no proceed with this bulletin.
Some customers may comment that the A/C blows hot air or is inoperative. They may also comment that they are unable to change the temperature or HVAC mode of the vehicle. Under these conditions, the actuator has moved to a default position. Refer to the table.
Cause
GM Engineering is seeing an increase in HVAC control head and actuator warranty where the component is fully functional when received. The root cause of the failure is intermittent wiring connections at the right hand BEC. Specifically, poor terminal tension of the 5V reference or Low Reference terminals in the X4 connector. Refer to the table.
After the fault is removed. the actuators recover once commanded.
Correction
DO NOT REPLACE THE CONTROL HEAD.
Use the following information to diagnose this condition:
The concern must be current before diagnosis can be performed.
Review and print the following SI documents - Electrical Center Identification Views, for use during diagnosis:
- Junction Block - Right I/P, Top View
- Junction Block - Right I/P X4
- Junction Block - Right I/P X5
Locate the Junction Block - Right Side IP on the vehicle.
For the appropriate actuator, measure the following signals for voltage/resistance from the BACK of the X4 or X5 connector and record the following:
DO NOT unplug the X4/X5 connector.
Turn Ignition On, A/C Blower Full, if possible - mode on "panel" and Temp to "cold."
Once the fault is removed, the actuator will stay in default position until commanded to a new position. Change commanded position regularly to see if the issue is still current.
Continue to monitor door positions (feedback) on Tech2 to see if it changes during circuit testing.
- Ignition Voltage - 12V
- Door Control Signal - 2.5V when stationary, OV when commanded toward "cold" or "panel", 5V when commanded toward "hot" or "defrost"
- Low Reference - less than 40 ohm with ignition on. Less than 10 ohm with ignition off
- Door Position Signal - measure voltage
- 5 Volt Reference - 5V
If any signals do not display the correct value or if the issue is corrected during testing, pull the connector and check the terminal for poor tension (use the appropriate terminal tool). Replace or repair the terminal if poor tension is found.
If all signals are correct at RH BEC, reconfirm the customer's comments.
If the condition is not present, no further repairs are necessary. If the condition is still present, recheck the actuator connector 5 volt reference circuit, pin drag test and repair connector/pin as necessary.
Warranty Information
For vehicles repaired under Enqineerinq direction, use the table.
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