LS1 · 2000 · COOLING / FAN CONTROL

2000 LS1 Cooling-Fan Diagnosis

Separate the 2000 LS1 PCM fan command from relay, motor, wiring and mechanical cooling-system failures.

APPLICATION: 2000 Firebird / Formula / Trans Am 5.7L LS1 (VIN G); exact-year 2000 cooling-system architecture.

SYMPTOMMake the failure repeatable.

TESTMeasure the system in the failed state.

ISOLATESeparate input, control, output and mechanical branches.

PROVEDemonstrate the failed branch before buying parts.

REPAIRRepair the proven cause.

VERIFYRepeat the same test state after repair.

Define what is wrong

Neither fan, one fan, wrong stage, fans always on, and engine overheating with fan operation are separate complaints.

Verify temperature input

Confirm ECT information is plausible and match the complaint state before deciding whether PCM fan command is appropriate.

Command vs output

Trace from PCM request through relay switching to fan motor power/ground. A missing command and a failed output stage require different repairs.

Mechanical cooling branch

Once fan operation is proven, diagnose coolant quantity/pressure, airflow, flow/thermostat and engine causes instead of continuing to replace electrical parts.

Modified-car checkpoint

Tune-based fan settings, thermostats, aftermarket fans/radiators and rewired relay kits can intentionally depart from stock behavior.

DO NOT REPLACE YET

Do not replace motors, relays, ECT sensor or PCM until the failed command/output branch is demonstrated.

FPV DIAGNOSTIC RULE

SYMPTOM → TEST → ISOLATE → PROVE → PARTS VERDICT → REPAIR → VERIFY. A DTC, gauge reading or symptom chooses the next test; it does not choose the part.

2000 starting/charging →2000 diagnostic architecture →Exact year navigator →Start over by symptom →

PUBLISHABLE SOURCE

Exact-year verification trail

2000 Pontiac Firebird LS1 service manual — Repair and Diagnosis

This page intentionally omits hard values that are not reproduced from an exact-year source on the page. Use the linked exact-year service information for connector-level tests, pinouts and numerical limits.

AFTER THE FAILURE IS PROVEN

Use the proven failed branch—not the original symptom—to choose the replacement. Go from diagnosis to the Parts Verdict →