This 1996 Pontiac Grand Prix came in on a hook with a no crank condition. In the automotive world a “no crank condition” is the starter does not work and a “no start condition” is the starter works but the engine will not run but I digress. The first I noticed when I tried to crank the engine was that the security light was flashing and of course the starter did not work.
I checked the key with an ohm meter.
It was good 2.36k ohms resistance. The system allows for a small variation in resistance values.
I located the VATS harness connector at the bottom of the dash.
Tested for a matching key resistance with the key in the ignition. Open circuit. Diagnosis of broken wire at the VATS lock cylinder inside the steering column. Note this vehicle demonstrated an open circuit with the key in the ignition and not even switched on. It may be necessary to fully rotate the ignition key cylinder to the crank position while monitoring resistance in order to find the problem. Many times the wire will not be completely broken and it will only go open when in the crank position.
I installed a bypass unit and cranked the vehicle. I also secured the wiring out of harms way.
Here is a list of factory resistance values for GM vehicles with the VATS system. The VATS system is identified by the ignition key having a resistor chip in the key as illustrated in the first picture. The above key with a resistance value if 2.36 K would match in the chart to a key blank #8. Since the car is a 1996 model it would have a letter code of ZB. This information is useful for buying a replacement key blank and having it cut for a new lock cylinder if you would like to properly repair your vehicle by replacing the faulty lock cylinder with a new part. The new lock cylinders do not come with a key that has a resistor in it. Instead it is a brass blank key with the proper tumbler code cut into it. The correct resistor key blank has to be purchased separately and it will have to have the tumbler code cut into it by a locksmith.
VATS# 93-95 96-00 Resistance
- Disc Disc .402 K Ohms
- CN YT .523 K Ohms
- FW JB .681 K Ohms
- GP EJ .887 K Ohms
- KA UR 1.13 K Ohms
- N5 Q3 1.47 K Ohms
- UN KH 1.87 K Ohms
- XB ZB 2.37 K Ohms
- GA QM 3.01 K Ohms
- NP YJ 3.74 K Ohms
- FY JH 4.75 K Ohms
- C5 ZR 6.04 K Ohms
- XY KM 7.50 K Ohms
- KB ET 9.53 K Ohms
- UW U3 11.8 K Ohms
Please excuse me if this is a stupid question. I have seen this theory in multiple places but I have not seen anyone really say where to actually put the resistor. If you could clarify that for me I would really appreciate it.
The bypassed resistor cannot cause the battery to go dead. If the rest of the systems are working correctly there will be no power on this circuit until the key is turned on.
I have a 91 Camero with this problem. I “solved” the no crank problem as many other have with a matched resistor inserted in the loop. My question now is around the potential for this “fix” to cause a slow battery drain. My car has gone through 2 batteries in the last three years and constantly needs jumping to start, especially after sitting for long periods. Could this bypassed resistor be a drain on the battery that could be causing my problems?
Camaro lovet/hater
The resistor bypass is only meant to bypass a faulty ignition lock cylinder which is the most common failure on GM VATS systems. However, there are cases where the TDM fails. From my experience the Lesabre and Park Ave seem to be the most affected by this. There are several manufactures of TDM bypass units and they work quite well. The original concept for these modules was to allow engines and computer systems from VATS vehicle to work when installed in non VATS vehicles (motor swaps).
Not sure why, but everybody around seem to keep calling “VATS Bypass” a simple resistor to install under your steering column or on the TDM’s connector. But the problem with that is it will only bypass the key and the lock cylinder, while the entire core of the security system (the TDM or Theft Deterrent Module) still remains in the loop! That trick was born just to add a remote starter and made sense when those cars where all new – no more the case today. …And guess what? It’s exactly the TDM that is well known to die with the age of the car – even before her 10th birthday. That’s what happened to my trusty Buick and is happening to other tens of thousands of unfortunate people in North America. Lots of people are even junking their cars since the time GM discontinued the production of the TDM back in Jan 2009.