Need GM Tech Help - Code 1626
Thread Starter
Burning Brakes
Joined: Sep 2001
Posts: 1,173
Likes: 1
From: Aguila AZ
Need GM Tech Help - Code 1626
'98 Corvette road race car.
This code hits and shuts the engine down due to loss of the fuel enable signal between the PCM and BCM. It is a security related code. I have verified all data link wiring curcuits, replaced the PCM and it still happens. Whenever I go WOT it shuts the engine down.
Since this is a repeatable event it rules out random issues. I think the condition is enabled by some combination of effects (theft protection?) that results in a 'Command' to shut off the fuel by interupting the fuel enable signal. The car will restart once the key is removed. Has anyone else had this problem and what was the fix? I have the GM tech manuals but I do not have a Tech II.
This is a road race car that has most unneeded systems removed for weight reduction. I have raced it in this condition for about a year before I started getting this problem. Not sure what has changed that would cause this code to set now.
If I could defeat or eliminate the security system to solve this problem I would do it...
I posted this in the scan and tune section, but I don't think it is a tuning issue so I reposted it here.
Shirl
This code hits and shuts the engine down due to loss of the fuel enable signal between the PCM and BCM. It is a security related code. I have verified all data link wiring curcuits, replaced the PCM and it still happens. Whenever I go WOT it shuts the engine down.
Since this is a repeatable event it rules out random issues. I think the condition is enabled by some combination of effects (theft protection?) that results in a 'Command' to shut off the fuel by interupting the fuel enable signal. The car will restart once the key is removed. Has anyone else had this problem and what was the fix? I have the GM tech manuals but I do not have a Tech II.
This is a road race car that has most unneeded systems removed for weight reduction. I have raced it in this condition for about a year before I started getting this problem. Not sure what has changed that would cause this code to set now.
If I could defeat or eliminate the security system to solve this problem I would do it...
I posted this in the scan and tune section, but I don't think it is a tuning issue so I reposted it here.
Shirl
Former Vendor
Joined: Feb 2004
Posts: 10,876
Likes: 8
From: Las Vegas NV
St. Jude Donor '06 & '12
Hopefully this will help.
DTC P1626 Theft Deterrent Fuel Enable Signal Lost
Circuit Description
The Vehicle Theft Deterrent system consists of the following components:
Powertrain Control Module (PCM)
Body Control Module (BCM)
Ignition Lock and Key
After the Body Control Module (BCM) has confirmed the key resistor pellet, the BCM sends a password to the PCM via the Class 2 Serial Data circuit. When this password matches the password stored in the PCM, the system enables the fuel. If the BCM does not send a password or if the PCM does not receive it, the vehicle will not start unless the PCM is in VTD Fail-Enabled mode. If the BCM and PCM loose communications with each other after the system has received the correct password, the PCM goes into VTD Fail-Enable mode. This allows the driver to restart the vehicle on future ignition cycles until communications between the BCM and PCM are restored. If the BCM and PCM loose communications before the PCM receives the BCM password, the PCM disables the fuel until communications is restored in order to prevent vehicle theft. In both cases DTC P1626 sets. The PCM will not disable the fuel injection once the PCM enabled the fuel within a given ignition cycle in order to prevent stalling as a result of VTD system faults.
Conditions for Running the DTC
The system has reached fuel enable decision point.
The PCM is in Failed Enable Mode due to loss of communications with the BCM after the system received the correct password earlier in the ignition cycle.
Conditions for Setting the DTC
The PCM does receive the password message from the BCM prior to the VTD Fuel Decision Point.
Action Taken When the DTC Sets
The PCM enables the fuel on future ignition cycles only if the PCM is in Failed Enable Mode.
The PCM stores the DTC information into memory when the diagnostic runs and fails.
The Malfunction Indicator Lamp (MIL) will not illuminate.
The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.
Conditions for Clearing the DTC
A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
A history DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
Use a scan tool in order to clear the DTC.
Diagnostic Aids
Important
Remove any debris from the PCM\TAC module connector surfaces before servicing the PCM\TAC module. Inspect the PCM\TAC module connector gaskets when diagnosing/replacing the modules. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM\TAC modules.
The most likely cause of DTC P1626 is a loss of serial data communication from the BCM. Check for a loss of power to the BCM or for other causes of communication loss. Check for the following intermittent conditions on the class 2 circuit:
Open Circuit
Grounded Circuit
Shorted to a voltage
Test Description
The numbers below refer to the step numbers on the diagnostic table.
A communication problem exists if the engine does not start and DTC P1626 sets. The PCM disables the fuel control if the PCM does not receive the password from the BCM before the engine is started.
The PCM in VTD Fail Enabled mode indicates that a communication problem occurred while the engine was operating. The engine will continue to operate if the PCM does not receive the password from the BCM while the engine is operating.
Check for an intermittent problem with the Class 2 circuit if the engine starts and idles.
Circuit Description
The Vehicle Theft Deterrent system consists of the following components:
Powertrain Control Module (PCM)
Body Control Module (BCM)
Ignition Lock and Key
After the Body Control Module (BCM) has confirmed the key resistor pellet, the BCM sends a password to the PCM via the Class 2 Serial Data circuit. When this password matches the password stored in the PCM, the system enables the fuel. If the BCM does not send a password or if the PCM does not receive it, the vehicle will not start unless the PCM is in VTD Fail-Enabled mode. If the BCM and PCM loose communications with each other after the system has received the correct password, the PCM goes into VTD Fail-Enable mode. This allows the driver to restart the vehicle on future ignition cycles until communications between the BCM and PCM are restored. If the BCM and PCM loose communications before the PCM receives the BCM password, the PCM disables the fuel until communications is restored in order to prevent vehicle theft. In both cases DTC P1626 sets. The PCM will not disable the fuel injection once the PCM enabled the fuel within a given ignition cycle in order to prevent stalling as a result of VTD system faults.
Conditions for Running the DTC
The system has reached fuel enable decision point.
The PCM is in Failed Enable Mode due to loss of communications with the BCM after the system received the correct password earlier in the ignition cycle.
Conditions for Setting the DTC
The PCM does receive the password message from the BCM prior to the VTD Fuel Decision Point.
Action Taken When the DTC Sets
The PCM enables the fuel on future ignition cycles only if the PCM is in Failed Enable Mode.
The PCM stores the DTC information into memory when the diagnostic runs and fails.
The Malfunction Indicator Lamp (MIL) will not illuminate.
The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.
Conditions for Clearing the DTC
A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
A history DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
Use a scan tool in order to clear the DTC.
Diagnostic Aids
Important
Remove any debris from the PCM\TAC module connector surfaces before servicing the PCM\TAC module. Inspect the PCM\TAC module connector gaskets when diagnosing/replacing the modules. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM\TAC modules.
The most likely cause of DTC P1626 is a loss of serial data communication from the BCM. Check for a loss of power to the BCM or for other causes of communication loss. Check for the following intermittent conditions on the class 2 circuit:
Open Circuit
Grounded Circuit
Shorted to a voltage
Test Description
The numbers below refer to the step numbers on the diagnostic table.
A communication problem exists if the engine does not start and DTC P1626 sets. The PCM disables the fuel control if the PCM does not receive the password from the BCM before the engine is started.
The PCM in VTD Fail Enabled mode indicates that a communication problem occurred while the engine was operating. The engine will continue to operate if the PCM does not receive the password from the BCM while the engine is operating.
Check for an intermittent problem with the Class 2 circuit if the engine starts and idles.
Thread Starter
Burning Brakes
Joined: Sep 2001
Posts: 1,173
Likes: 1
From: Aguila AZ
Jeff, Thanks for the info. I have all the same info in the GM tech manuals. The Tech info is slanted towards a problem with wiring, connectors and component failure. I have tested everything I can without a Tech II. Since everything checks out okay I think the problem is with something in the security system that commands a fuel cutoff to protect against theft.
What I'd like to know is what conditions does the security system look at that would trigger a fuel cutoff. It could be something as simple as a faulty door lock or hatch switch or VATS problem. If I knew where to look, I could fix the problem...
Shirl
What I'd like to know is what conditions does the security system look at that would trigger a fuel cutoff. It could be something as simple as a faulty door lock or hatch switch or VATS problem. If I knew where to look, I could fix the problem...
Shirl
