I have a 98 monte carlo 3.1 auto trans. when i turn the key to start, the security light flashes and it does nothing I tried a second key and no luck. I found the tdm relay and i have current to the two yellow wires when i try to start,but not the yellow and black wire. I can jump from one of the hot wires to the purple one and it will crank but only run for a second then shut off. I suspect the problem is with the tdm module or the ignition switch. What is the best way to diagnos this

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Have it checked for DTC'S - diagnostic trouble code's . I suspect the problem is with the tdm module or the ignition switch ???? Assuming will only get you into trouble . If the PCM - engine computer does not see the right coded meassage from the TDM it won't turn on the fuel injectors or it will cut them off in two seconds . .
Buick Security Systems 1998 Chevy is the same .
Ignition Key With Wrong Resistor Pellet Code is Used To Start Engine
The theft deterrent module performs one of the two following actions when you attempt to start the vehicle with a wrong ignition key:
• There are 15 PASS-Key® II resistance ranges. The PASS-Key® II resistance may be one of the 14 valid but incorrect PASS-Key® II resistance ranges. The theft deterrent module will perform the following actions when you attempt to start the vehicle (if the condition is present during an engine start attempt or for 1 second any time after the engine has started):
• Turns on the SECURITY indicator
• Sends a password to the PCM through the fuel enable signal circuit
• The password disables fuel delivery to the engine.
• Disables the theft deterrent relay, which disables the starter circuit
• Disables sampling of the PASS-Key® II resistance for 3 minutes
• The 3 minute time period is called the shut-down period.
• Disconnecting the battery will not clear the timer sequence. The timer sequence will resume when battery power is restored.
• Inserting the proper key during the vehicle shut-down period will not start the engine. The engine will not start until the shut-down period has elapsed.
• After the shut-down period, the engine will start if the correct ignition key resistor pellet is used.
• The PASS-Key® II resistance may be correct and allow the engine to start. Later during the same ignition cycle, the PASS-Key® II resistance may be one of the 14 valid but incorrect resistance ranges. The theft deterrent module will perform the following actions:
• Enters the fail-enable mode
• Turns ON the SECURITY indicator
• Sends a password to the PCM through the fuel enable signal circuit when more attempts to start the engine occur
• The password allows the fuel enable circuit to deliver fuel to the engine.
• Enables the theft deterrent relay, which also enables the starter circuit.

Ignition Key With Correct Resistor Pellet Code is Used To Start Engine
The theft deterrent module performs the following actions when the correct ignition key is used in order to start the vehicle:
• Enables the theft deterrent relay. The theft deterrent relay enables the starter unit.
• Sends a password to the Powertrain Control Module (PCM) through the fuel enable signal circuit. As a result, the PCM allows fuel delivery to the engine.


By pass theft system .
GM VATS Key Resistor Key Security Bypass
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