Diagnosing P1637

Hi everyone,

I have a 2002 Camaro 5.7 and I have a code P1637 for the alternator.  I noticed the red wire on the connector was broken off from the back of the alternator.  I replaced the connector and wire and code P1637 still appears.

I tested the charging system and it passed and no battery light comes on.  

I used a test light to test the red wire from the alternator and the test light doesn't light.  Should there be full-time power on the red wire when the engine is running?

 

I used a test light to test the red wire from the alternator and the test light doesn't light.  Should there be full-time power on the red wire when the engine is running?

The test light not lighting on the red wire is normal.

The Generator L circuit on your Camaro will be supplied with voltage from the PCM to get the alternator to start charging. I've usually found that voltage to be 5.0V, but service info for P1637 is looking for 10.0V or more. But it's not a true 'power', it's just signal voltage and won't carry any actual current. That's why the test light didn't light.

There's a key test provided in the P1637 flow chart:

 

Your Actron scanner won't have the 'GEN L–Terminal Signal' PID, but you can still check for voltage on the red wire, alternator plugged in and engine idling.

 I do have another scan tool. I pulled up the Generator L data pid and there's no data voltage shown (blank) and no activity on the graph. So possibly there's a break in the red wire somewhere in the harness to the pcm or a missing/bad ground?