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Engine Cranks But Won't Statr

1995 Buick LeSabre with 6 cyl fuel injection. Engine cranks, starts to run, but shuts down in half second or less. Problem was intermittent in past but now hasn’t started in over 100 tries (many different days)

My wild guess would be the fuel pump, but there’s really no way to tell without at least finding out if you’re losing spark or fuel.

The problem might be with the ignition module. Ignition modules function in two modes. These are the start and run modes.

During the start mode, the ignition module allows full battery voltage to the ignition coils. This ensures a cold engine starts when the fuel mixture is the richest. When the ignition switch is allowed to go the the run position, the ignition module goes into the run mode. It’s here where the ignition module drops the voltage to the ignition coils because it takes less voltage to keep the engine running. And this also saves wear and tear on the secondary ignition components.

So the problem could be that the ignition module is functioning during the start mode, but failing in the run mode.

Tester

I plugged in a code reader that returned “VATS” system failure and a “pass code” problem. This led me to numerous other web sites that said the Theft Deterrent Module (TDM) was well known to cause the exact symptom I am seeing if the module fails internally or if contacts in the ignition switch can’t read the resistor pellet embedded in the key. The TDM is supposed to enable a relay in the circuit to the starter solenoid AND send a 30-60 Hz square wave pulse to the ECM allowing the ECM to command the fuel injectors to operate. TDM isn’t supposed to allow cranking but no injector, so may be failure of TDM or ECM. Numerous posters said dealer fix of the problem usually goes around $1,000.