Mechanics

CHEVY SECUIRTY LIGHT WON'T START PROBLEM

2008 Chevrolet Express

Engine Performance problem
2008 Chevy Express 6 cyl Two Wheel Drive Automatic 80000 miles

I have a 2008 Chev full size van every once in awhile it will not start no matter what. The dash " secuirty" lite comes on. I have herd it is a secuirty shut down it sounds like it shuts the fule off just as it is starting. I was told to wait 20 min and then it will reset, that worked for me once. NOw I have my guys 150 miles away on a construction site in the hills and the truck will not start. I have been told that there is a wire Ican cut but only when it is in this security condtion I want to know what wire that is. I cannot afford this my guys are mad and it is costing me more then I can possible make off the job. I do not care about the security car theft alarm I can live with out it but I have a three year old truck that I am afraid to use. HOw do I get this disconnected?
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Rod Durham
March 18, 2010.




Hello. Thanks for the donation. Much appreciated.

There is no magic fix for this i'm afraid. No wires to cut. And you cannot disable the immobolizer system. Tje only way is to have the vehicle plugged into a diagnostic computer to retrieve the fault codes and repair the fault. Sometimes leaving the key in the ignition with ignition on will reset the system.

Immobilizer Description and Operation
The immobilizer system functions are provided by the theft deterrent module (TDM) and the engine control module (ECM). When an ignition key is inserted into the ignition lock cylinder and the ignition is switched ON, the transponder embedded in the head of the key is energized by the exciter coil surrounding the ignition lock cylinder. This exciter coil is part of the TDM. The energized transponder transmits a signal that contains its unique value, which is received by the TDM. The TDM then compares this value to a value stored in memory. If the values match, the TDM will send the prerelease password via the serial data circuit to the ECM. If the transponders unique value is incorrect, the TDM will send the fuel disable password to the ECM.
When the ECM receives the TDM prerelease password, the ECM will challenge the password. The ECM sends this challenge back to the TDM via the serial data circuit. Both the ECM and TDM perform a calculation on this challenge. If the calculated response from the TDM equals the calculation performed by the ECM, the ECM will allow vehicle starting.
The components of the theft system are as follows: TDM
ECM
Ignition key (Transponder)
Security indicator

Theft Deterrent Module (TDM)
Vehicles with steering column mounted ignition switches have the exciter integral with the theft deterrent module (TDM), which is located within the steering column. The TDM can learn up to 10 keys (transponder values).
The TDM uses the following inputs: battery voltage, ignition switched voltage and ground circuit. The theft deterrent control module uses the following outputs: password exchange and challenge/response with the engine control module (ECM).
When an ignition key is inserted into the ignition lock cylinder and the ignition is switched ON, the transponder embedded in the head of the key is energized by the exciter coils surrounding the ignition lock cylinder. The energized transponder transmits a signal that contains its unique value, which is received by the TDM. The TDM then compares this value to the learned key code stored in memory. The TDM then performs one of the following functions: If the transponder value matches the values stored in the TDM memory, the TDM will send the prerelease password to the ECM via the serial data circuit.
If the transponders unique value does not match the value stored in the TDM, the TDM will send the fuel disable message to the ECM via the serial data circuit.
If the TDM is unable to measure the ignition key transponder value, the TDM will not send any messages to the ECM.
Engine Control Module (ECM)
When the engine control module (ECM) receives the theft deterrent module (TDM) prerelease password, the ECM will challenge the password. The ECM sends this challenge back to the TDM via the serial data circuit. Both the ECM and TDM perform a calculation on this challenge. If the calculated response from the TDM equals the calculation performed by the ECM, the ECM will allow vehicle starting.
The ECM will disable vehicle starting if any of the following conditions occur: The prerelease password is invalid.
The fuel disable password is sent by the TDM.
No passwords are received-There is no communication with the TDM.
The TDM calculated response to the challenge does not equal the calculation performed by the ECM.
The Ignition Key (Transponder)
The ignition key for Passkey III+ (PK3+) equipped vehicles is a standard ignition key with a transponder located in the plastic head of the key. The transponder value is fixed and unable to be changed. The immobilizer system uses the ignition key transponder value to determine if a valid ignition key is being used to start the vehicle. There are approximately 3 trillion possible transponder values. There are no visible electrical contacts. The keys are identified by + symbol in a circle stamped into the steel shank of the key. The immobilizer system use the following types of ignition keys: Master Keys
Master keys have a black plastic head for full access operation of the vehicle. Master keys may perform the following functions: Start the vehicle.
Lock/unlock all of the door locks and rear compartment.
Lock/unlock all of the storage compartments.
Valet Keys
IMPORTANT: Valet keys are NOT standard equipment on all GM vehicle lines.

Valet keys have a gray plastic head and are for restricted operation of the vehicle. Valet keys may perform the following functions: Start the vehicle.
Lock/unlock all of the door locks.
Fleet Keys
IMPORTANT: Fleet keys are NOT standard equipment on all GM vehicle lines.

Fleets keys allow full access to the vehicle just as a master key would. However, unlike a master key which may only learn 10 keys to a particular vehicle, an unlimited number of fleet keys may be learned to the vehicle. Fleet keys are only used in vehicles configured for fleet use with RPO 6E2 or 6E8.
Start the vehicle.
Lock/unlock all of the door locks and rear compartment.
Lock/unlock all of the storage compartments.
Security Indicator
The theft deterrent module (TDM) can command the instrument panel cluster (IPC) to illuminate the security indicator only when the ignition key is in the ON position. The TDM will command the security indicator be illuminated any time a fault is noted in the immobilizer system and when the engine starting is disabled.
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Dave H
Mar 18, 2010.
I just had the same problem on my 98 Express Van. Found out thathe wires for the Antitheft wiring harness runs under the steering wheel cover from left to right and was chafed bare until the wire touched ground. My mechanic taped the wire up, replaced the blown fuse and I was running in seconds. It seems the wiring harness is stretched so tight and rubs the steering column support brace that when you tilt the steering wheel up and down, this ca cause chafing. I'm not saying this is the problem, but it is worth looking at. Only 2 screws hold the steering column covers together. My mechanic told me also if you have a no start to turn on the key to on-press the accelerator pedal to the floor 5 times as fast as you can and then turn the key to on. The ecm(computer) is reset, and if there is not a mechanical problem preventing the engine from starting, it should start. It will run roughly be Hopew this helps. Cause the computer has to "learn" engine responses again.

Tiny
Coastiesteve
Jan 3, 2011.

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