Alternator FR Signal Circuit Troubleshooting

Disconnect the ALT 4P connector.
Turn the ignition switch ON (II).
Measure voltage between ECM/PCM connector terminals A24 and B13.

Fig 1: Measuring Voltage Between ECM/PCM Connector Terminals A24 & B13

Is there about 5 V?
1. YES - Go to step 4.
2. NO - Go to step 14.
Turn the ignition switch OFF.
Reconnect the ALT 4P connector.
Start the engine. Hold the engine at 3,000 RPM with no load (in Park or neutral) until the radiator fan comes on, then let it idle.
Measure voltage between ECM/PCM connector terminals A24 and B13.
Does the voltage decrease when the headlights and rear window defogger are turned on?
1. YES - The ALT FR signal is OK.
2. NO - Go to step 8.
Turn the ignition switch OFF.
Disconnect the negative cable from the battery.
Disconnect ECM/PCM connector B (24P).
Disconnect the ALT 4P connector.
Connect the ALT 4P connector terminal No. 4 and body ground with a jumper wire.

Fig 2: Connecting ALT 4-Pin Connector Terminal No. 4 & Body Ground
Check for continuity between body ground and ECM/PCM connector terminal B13.

Fig 3: Checking Continuity Between Body Ground & ECM/PCM Connector Terminal B13

Is there continuity?
1. YES - Test the ALT (see step 1 on ALTERNATOR AND REGULATOR CIRCUIT TEST ).
2. NO - Repair open in the wire between the ECM/PCM (B13) and the ALT.
Turn the ignition switch OFF.
Disconnect the negative cable from the battery.
Disconnect ECM/PCM connector B (24P).
Check for continuity between body ground and ECM/PCM connector terminal B13.

Fig 4: Checking Continuity Between Body Ground & ECM/PCM Connector Terminal B13

Is there continuity?
1. YES - Repair short in the wire between the ECM/PCM (B13) and the ALT.
2. NO - Reprogram the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM, then recheck (see ECM/PCM REPROGRAMMING AND SUBSTITUTION FOR TESTING ). If the symptom/indication goes away with a known-good ECM/PCM, replace the original ECM/PCM.