I have an '04 Z06 with a three month old AC/Delco professional series 7yr battery.

Everything is going well and I then notice a "Service vehicle soon". message.

I clear it, but when I stop and restart, I get "Charging system fault" and then "Service vehicle soon".

I clear all codes from the DIC, but every time I restart I get "Charging system fault" followed by "Service vehicle soon".

Every time I check the codes, I have a P1637H.

I must have cleared it five times, and just starting it after clearing the codes, the same messages and the same code left in the DIC.

I went back to the car after it sat for a week.

The battery was 12.2 volts

I start the car with no accessories on:
Battery: 14.5
Alternator output: 14.6 (measured at large red wire on alternator)
Dash volt gauge: 14.2

I then turn on the radio, AC fan to high, & headlights
Battery: 14.3
Alternator output: 14.6
Dash volt gauge: 14.0


Sure seems like all is well with the charging circuit?

Any ideas?

Thanks in advance

 

Found this article hope it helps out.

http://www.gearchatter.com/viewtopic10125.php

 

Wow... thanks... that totally helps.

Now at least I know what I'm dealing with... I didn't have a clue what the L-terminal circuit was or why it existed.

 

This may be a better explanation of the code than Gearchatter has. The description shown in their write up hasn't been used since the 2000 model year. The diagnostic procedure is different as well.

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

• Key ON Test
• The Key is in the ON position for 5 seconds.
• The engine is OFF.

• Engine Run Test
• The engine is running.
• The engine speed is less than 3000 RPM.

Conditions for Setting the DTC

1. Key ON Test The ECM detects a high signal voltage on the generator turn on signal circuit for at least 5 seconds.
2. The engine must be started.

During the RUN test, the ECM detects a low signal voltage on the generator turn on signal circuit for at least 5 seconds.
Action Taken When the DTC Sets

• The ECM sends a class 2 message to the IPC to illuminate the charge indicator and/or turn on a message.
• The ECM will not illuminate the malfunction indicator lamp (MIL).
• The ECM will store the conditions present when the DTC set as Fail Records data only.

Conditions for Clearing the MIL/DTC

• The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
• The DTC can be cleared by using the scan tool Clear DTC Information function.

Step
Action
Value
Yes
No
Schematic Reference: Starting and Charging Schematics
Connector End View Reference: Engine Controls Connector End Views in Engine Controls-5.7L, Power and Grounding Connector End Views in Wiring Systems, or Engine Electrical Connector End Views
1
Did you perform the Engine Electrical Diagnostic System Check?
--
Go to Step 2
Go to Diagnostic System Check - Engine Electrical

2

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. Wait 5 seconds.
4. Start the engine.
5. With a scant tool, monitor the DTC information for DTC P1637 in Engine Controls.

Does the scan tool indicate that DTC P1637 has passed?
--
Go to Testing for Intermittent and Poor Connections in Wiring Systems
Go to Step 3

3

1. Turn Off the engine.
2. Disconnect the generator harness connector.
3. Start the engine.
4. Measure the voltage between the generator turn on signal circuit and ground.

Does the voltage measure near the specified value?
5.0 V
Go to Step 5
Go to Step 4
4
Test the generator turn on signal circuit for a short or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 11
Go to Step 5
5
Test the generator battery positive voltage sense circuit for a high resistance or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 11
Go to Step 6
6
Test the generator battery positive voltage output circuit for a high resistance or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 11
Go to Step 7
7
Inspect for poor connections at the harness connector of the generator. Refer to Connector Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 11
Go to Step 9
8
Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 11
Go to Step 10
9
Replace the generator. Refer to Generator Replacement .
Did you complete the replacement?
--
Go to Step 11
--
10
Important

The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement in Engine Controls 5.7L.
Did you complete the repair?
--
Go to Step 11
--

11

1. Use the scan tool in order to clear the DTCs .
2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?
--
Go to Step 3
System OK



Bill

 

Thanks Bill.... you were 100% correct (as usual). I went to the dealer since I have a GMPP warranty. They printed out the exact procedure you posted here.


I had checked all that I could, and it appeared to be the PCM. I hate going to the dealer without at least having a couple ideas about what they will/may do to my car...

They too found the problem was the PCM and replaced it under warranty.

Thanks all......