I just went through an issue with my alternator not charging and it turned out that the small cable from the harness to the alternator had broken. I fixed this and it was giving just over 13 volts at idle. On my commute today I noticed however the voltage climbing towards the 18V side and the check gauges light came on. It was also rpm dependent. higher rpm gave higher voltage. So now it appears to be giving too much voltage. Ive tried a search to no avail. Any ideas on what this could be?

 

The PCM controls the regulator. The code for this is a hidden code and doesn't set a CEL. You'll need a higher end scanner to read it or clear it.

Double check the connection and wire. I can't remember off hand with pinout it is but I'll look into it again.

 

Here's the DTC info.

DTC P1637

Circuit Description

The powertrain control module (PCM) uses the generator turn on signal circuit to control the generator. A high side driver within the PCM allows the PCM to turn the generator ON and OFF. When Generator operation is desired, the PCM sends a 5 volt signal to the voltage regulator via the generator turn on signal circuit. This causes the voltage regulator to begin controlling the generator field circuit. Once the Generator is enabled by the PCM, the voltage regulator controls generator output independently of the PCM. Under certain operating conditions, the PCM can turn Off the generator by turning Off the 5 volt signal on the generator turn on signal circuit. The PCM has fault detection circuitry which monitors the state of the generator turn on signal circuit. If the fault detection circuit senses a voltage other than what is expected, this DTC will set. The voltage regulator also contains fault detection circuitry. If the regulator detects a problem, the regulator will ground the generator turn on signal circuit, pulling the voltage low. This also causes the PCM to set the DTC.

Conditions for Running the DTC
The ignition is on.
System voltage between 9.0 and 18.0 volts.

Conditions for Setting the DTC

An improper voltage level has been detected on the alternator lamp driver circuit.

Above conditions for at least 30 seconds.

Action Taken When the DTC Sets

The PCM will not illuminate the malfunction indicator lamp (MIL).

The PCM will store conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.

Conditions for Clearing the MIL/DTC

A History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

The DTC can be cleared by using a scan tool.

 

The pinout for the GEN L-terminal from Alt is the Red 15.

 

I have VCM Scanner from hptuners, would that be able to read that DTC?

 

I also want to mention that I had the alternator tested yesterday and it came back good. If the voltage regulator was bad on the alternator, shouldn't that have come up on the test?

 

HPT will read that code and clear it.

Testing the Alt at your local parts store doesn't test the Gen L-terminal. The only way I found that tests it is a tech 2 or high dollar scanner that can activate it.

 

I noticed yesterday that the symptom would come and go. If I took a really hard turn it could start over charging but then turn again or hit a bump and it would go back to normal, so im guessing something is loose and is messing with the connection. Where should I start to look? could it be the small red wire?

 

Yes. The connector may be bad or terminal loose It's only a 20ga wire and thin as hell.