P1637 H - Generator L - Terminal Circuit
 

has anybody had this code????

You should fill in your profile so somebody knows what year vette you are talking about and the transmission type and body type.

Hard to guess what's going on from your lack of description.

The code based on a 2001 per the manual refers to the Output Drivers Module (ODM) and is interfaced with the PCM.

Could be caused by a bad or dirty connection. I would try resetting the DTC and see if the code re-appears.

If it does check your PCM connections and grounds.

99 frc

The PCM monitors the alternator through the red and grey wires

The L-terminal circuit from the generator is a discrete circuit (a discrete circuit has no splices and only one source and destination) into the PCM. The PCM applies ignition voltage to the generator L-terminal circuit. A small amount of current flows from this circuit through the generator windings to ground to create a magnetic field which starts the generator process. When the generator is at operating speed and producing voltage, a solid state switch for the L-terminal circuit in the generator opens and the PCM detects that the initial startup current flow has stopped.

The PCM expects to detect low voltage on the L-terminal circuit prior to the generator rotating at operating speed and conversely expects the circuit to be at ignition voltage potential when the generator is operational. When the PCM detects a fault (circuit shorted to ground, or circuit shorted to voltage), the Driver Information Center will display Charging System Fault.

The generator has an input to the PCM called the F Terminal to indicate the percentage of total capacity that the generator is producing. This signal is detected by the PCM as a duty cycle from the generator and displayed on the scan tool as a percentage. The PCM can monitor the generators output under all conditions to determine if it is functioning normally.

When there is low demand from the electrical system on the generator, a low duty cycle percentage will be displayed. As more accessory load is placed on the generator, the duty cycle output detected by the PCM will approach 100 percent. A normally functioning generating system will never reach 100 percent as indicated on the scan tool.

The L and F terminals are the red and grey

I hope this clears up your inquiry
Bill aka ET

:eek: :eek: :eek:

Yes, I had this code when a ground wire was inadvertently left loose after a header install. When the ground got retightened, the fault went away.

Short to ground

Since the code was P1637 H, the good news is that you do not currently have this problem but the bad news is it may come back, if only for a long enough time to trigger the code again.

I first got the P1637 code 18 months ago and have been trying to permanently get free of it ever since. At times, it will go away for months but it always comes back.

Using my service manual, Tech2, test lamp and DMM, I have followed the diagnostic procedure so many times I don't need the book anymore. I have inspected, cleaned and tightened all connections several times to no avail. For awhile, I had the charge system fault message as well but cleaning the connection at the starter solved that.

The one abnormality that has remained constant is that the "generator sense circuit", which is the S terminal on the generator will not light a test lamp as it is supposed to do. Unfortunately, I can find no info in the manual as to the remedy, nor a diagram of it.

The output of the generator at the output terminal has always been normal. I have come to the point where I'll either choose to ignore the code or replace the engine wiring harness, which is very expensive.

Hopefully, your code won't come back or if it does, You'll be able to solve it easily :cheers: