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.
2000 Isuzu Trooper LS V6-3.5LFACTORY OEM SERVICE PROCEDURE
Shift Light: Testing and Inspection
Upshift Lamp System Check (Manual Transmission Only)
Circuit Description
The shift lamp indicates the best transmission shift point for maximum fuel economy.
The lamp is controlled by the Power Train Control Module (PCM) and is turned "ON" by grounding the BLK wire.
The PCM is used information from the following inputs to control the upshift lamp.
- Engine Coolant temperature (ECT) Sensor
- Throttle Position Sensor
- Vehicle Speed Sensor
- Engine Speed
The PCM uses the measured RPM and the vehicle speed to calculate what gear the vehicle is in. Its this calculation that determines when the upshift lamp should be turned "ON".
Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed-through wire insulation. Check for poor connections or a damaged harness.
Inspect the PCM harness and connector for proper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
Test Description
1. This should not turn "ON" the up-shift lamp. If the lamp is "ON", there is a short to ground in BLK or a fault PCM.
2. This checks the upshift lamp circuit up to the PCM connector.
If the up-shift lamp illuminates, then the PCM connector is faulty or PCM does not have the ability to ground the circuit.
Circuit Description
The shift lamp indicates the best transmission shift point for maximum fuel economy.
The lamp is controlled by the Power Train Control Module (PCM) and is turned "ON" by grounding the BLK wire.
The PCM is used information from the following inputs to control the upshift lamp.
- Engine Coolant temperature (ECT) Sensor
- Throttle Position Sensor
- Vehicle Speed Sensor
- Engine Speed
The PCM uses the measured RPM and the vehicle speed to calculate what gear the vehicle is in. Its this calculation that determines when the upshift lamp should be turned "ON".
Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed-through wire insulation. Check for poor connections or a damaged harness.
Inspect the PCM harness and connector for proper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
Steps 1 - 3:
Steps 4 - 14:
Step 15:
Test Description
1. This should not turn "ON" the up-shift lamp. If the lamp is "ON", there is a short to ground in BLK or a fault PCM.
2. This checks the upshift lamp circuit up to the PCM connector.
If the up-shift lamp illuminates, then the PCM connector is faulty or PCM does not have the ability to ground the circuit.
Factory Service Tools
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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.