Applies to: 2002 Firebird / Trans Am with the LS1, unless a step below says otherwise.
First prove which fan speed is missing. The 2002 system uses two fan motors and three relays, so one failed mode does not mean both motors are bad.
PAGE SCOPELS12002Use this page only for the model-year/application stated here unless another year is explicitly identified in the published material.
Start here
Perform this test exactly as shown, record the result, then use PASS or FAIL to return to the diagnostic tree.
Confirm this page matches the vehicle and symptom before testing.
Gather the tools listed on the page before disconnecting anything.
If a STOP warning appears, do not improvise past it.
After a repair, repeat the failed test before moving on.
PASS — The test result is in range or the commanded function works.
FAIL — The result is outside the expected condition; follow that branch.
STOP — The next step needs information/equipment not safely covered here.
Diagnostic Progress0 steps complete
Diagnostic Workpad
Write down the actual measurement before choosing PASS or FAIL. This keeps one bad assumption from steering the rest of the diagnosis.
Your notes stay in this browser on this device. They are not sent to F-Body Parts Verdict.
Ready
STEP 1
Command low-speed fan operation
DO THIS
Ignition ON, engine OFF as appropriate for the scan-tool output test. Command the fan low-speed state ON and OFF and observe both fans.
YOU SHOULD SEE
Both fans respond in the commanded low-speed mode.
PASS → Low speed works. Continue to high-speed command.
FAIL → Stay in the low-speed relay/motor/power/ground branch. Do not shotgun all three relays.
STEP 2
Command high-speed fan operation
DO THIS
Before commanding the next fan state, allow the short delay required by the supplied procedure; then command high-speed ON and OFF and observe both fans.
YOU SHOULD SEE
Both fans respond in high-speed mode.
PASS → Both commanded modes work. Fan hardware/relay operation is supported; return to overheating diagnosis.
FAIL → Use the exact 2002 fan schematic to isolate the failed relay path, motor feed, ground or connector. The supplied tree uses fused jumper checks after identifying the failed mode.
The service procedure notes a roughly 3-second delay when changing commanded fan speeds.
After a repair: repeat the test that failed before calling the car fixed. Then verify the original symptom is gone.
STAY IN THE CORRECT APPLICATION
2002 LS1: related published paths
These links keep you in the same exact-year engine material where available. Do not carry hard numbers, pinouts or thresholds to another year unless that page explicitly says they are shared.