Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
SYS.OK|MANUAL.DB● LIVE
HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1795 (HVAC SYSTEM - MANUAL)DIAGNOSTIC INFORMATION AND PROCEDURESDTC P255FCIRCUIT SYSTEM TESTING
2003 Chevrolet TrailBlazer 4.2 S, 4WD
Circuit System Testing
2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Circuit System Testing
WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
- Ignition OFF, disconnect the HVAC harness connector at the a/c switch.
- Test for less than 1.0 ohm of resistance between the HVAC control module ground circuit terminal C1 pin 12 and ground.
- If greater than the specified range, test the ground circuit for an open/high resistance.
- Ignition ON, verify the scan tool ECM A/C request parameter is No or open.
- If not the specified value, test the a/c request signal circuit terminal HVAC control module terminal C1 pin 8 for a short to ground. If the circuit tests normal, replace the HVAC Control Module.
- Install a 3A fused jumper wire between the signal circuit terminal C1 pin 8 and the ground circuit terminal C1 pin 12. Verify the scan tool ECM a/c request switch parameter is YES or closed.
- If not the specified value, test the a/c request signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
RENDER: 1.0x
NO RELATED
Recommended Tools & Savings
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.