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I've got a 1993 z28 6 speed that rarely gets driven. It ran last year just fine. Put a new battery in it this year and got no crank from the starter. I put my scanner on the car and got codes 16 and 46. I did some research and think I have a vats problem. I ohmed out the key and it's 7.36 ohms. Pulled the connector apart under the dash and got the same ohms when the key is in the ignition. Thinking that maybe I needed 7.5 ohms I bought a gm vats bypass resistor kit and tried the 7.5 ohm resistor and still got no crank. I have read that the 93 model year is a little different than the rest in that generation. The security light on the dash never lights up with key in run or when I try to crank. I'm thinking I need to do a vats system bypass. What would be the most simple way to go about doing that, and remember it's a 93, so maybe different than other models. Any info or tips are appreciated.
If you used a 7.5 ohm resistor, it's not going to work. There's something wrong with your resistance measurements.
The range for key resistor pellet #3 is low limit - 681 ohms, high limit - 728 ohms. What range did you set the ohm meter on - maybe 100X? Sounds like you were at the very edge of the high range. Clean the contacts on the pellet, and measure it again using the correct scale on the meter.
Since the "SECURITY" light does not come on and stay on for 3 minutes when you try to start the engine, the key resistance does not appear to be the problem.
Since the "SECURITY" light does not flash at a rate of 1 flash per second, the circuit that reads the key pellet does not appear to be the problem.
The only difference between the 93 and later model PASS-Key II system is the frequency that the theft deterrent module (TDM) sends to the ECM to allow the fuel system to start is 30Hz, while later models are 50Hz.
DTC 16 indicates that while cranking the engine the ECM did not see the low resolution cam position pulse signal from the Optispark. The ECM cannot start the engine without that signal. However, this must be a "stored" code, since the ECM cannot send that signal unless the starter is cranking the engine.
DTC 46 indicates the 30Hz "fuel enable" signal is not reaching the ECM. If the code is "stored" and the engine will not crank, the problem is an incorrect key or starting procedure - per the factory service manual.
Unfortunately, the above diagnosis contains a contradiction. You need to start over, measuring the key resistance correctly.
I'm sorry,
I should have been more precise when I explained the ohm readings. The key pellet measures 7.36k ohm on my multimeter and I only have one selector spot for ohms on my meter. I correctly pulled the wires apart under the steering column and measured exactly the same 7.36k ohm with the key in the ignition. This should rule out the key or key cylinder being bad, unless my key pellet is supposed to measure the 7.56 k ohm that came in my gm vats resistor kit. I did make a connector with ends and soldered in the 7.56
k ohm resistor. I plugged it into the correct end under the dash and got no crank, no security light. Also cleared codes and tried to restart and same codes came up. Codes 16 and 46.
Does the “SECURITY” light come on during the 3-second bulb check when you turn the key to “RUN”?
The corrected resistance measurements indicate they are within the acceptable limits for key #13. The limits of the resistor reading is clearly shown in the table I linked above. It’s directly out of the factory service manual.
When you installed the bypass resistor, did you either unplug the connector for the key cylinder, or cut the wires - sounds like you built a new connector for the resistor, and plugged in that connector, in place of the connector from the lock cylinder. Please confirm. If the key cylinder wiring is still intact, and the bypass resistor is in the circuit, the combined resistance of the two resistors in parallel is outside the acceptable limits for key #13.
Appears you have verified the key and wiring from the cylinder is good, at least to the harness connector. Now you have to verify the circuit from the connector to the theft deterrent module (TDM). Assuming the “SECURITY” bulb is working, since it doesn’t light up when you turn the key to “START”, the wiring would appear to be OK.
That brings us to the TDM. If the key resistance is correct, the TDM should do 2 things:
- Send a ground to the signal side of the theft deterrent relay (TDR) and the relay completes the circuit to the starter. However, there is another switch in the starter circuit. With the T56 there is a switch on the clutch pedal assembly that completes the circuit on the load side of the relay when the clutch is depressed. A failed TDM, a failed TDR, or an inoperative clutch switch can prevent cranking.
- Send the “fuel enable” signal to the ECM in order to activate the injectors. The fact you have DTC 46 appears to indicate the ECM is not receiving the “fuel enable” system. I wasn’t aware it would send that signal if the engine wasn’t cranking.
Does the “SECURITY” light come on during the 3-second bulb check when you turn the key to “RUN”?
The corrected resistance measurements indicate they are within the acceptable limits for key #13. The limits of the resistor reading is clearly shown in the table I linked above. It’s directly out of the factory service manual.
When you installed the bypass resistor, did you either unplug the connector for the key cylinder, or cut the wires - sounds like you built a new connector for the resistor, and plugged in that connector, in place of the connector from the lock cylinder. Please confirm. If the key cylinder wiring is still intact, and the bypass resistor is in the circuit, the combined resistance of the two resistors in parallel is outside the acceptable limits for key #13.
Appears you have verified the key and wiring from the cylinder is good, at least to the harness connector. Now you have to verify the circuit from the connector to the theft deterrent module (TDM). Assuming the “SECURITY” bulb is working, since it doesn’t light up when you turn the key to “START”, the wiring would appear to be OK.
That brings us to the TDM. If the key resistance is correct, the TDM should do 2 things:
- Send a ground to the signal side of the theft deterrent relay (TDR) and the relay completes the circuit to the starter. However, there is another switch in the starter circuit. With the T56 there is a switch on the clutch pedal assembly that completes the circuit on the load side of the relay when the clutch is depressed. A failed TDM, a failed TDR, or an inoperative clutch switch can prevent cranking.
- Send the “fuel enable” signal to the ECM in order to activate the injectors. The fact you have DTC 46 appears to indicate the ECM is not receiving the “fuel enable” system. I wasn’t aware it would send that signal if the engine wasn’t cranking.
1.The security light does not come on with the 3 second bulb check when the key is turned to run. Brake light, along with check engine light are the only lights that come on.
2. I built a new connector and connected into the correct side of the plug eliminating the need for the pellet key, but I see now my pellet key is within the limits, so I removed the plug and plugged factory ends back in. I cannot confirm the wiring is good all the way to the TDM. I cannot seem to find a picture of what the TDM looks like. I believe it's located passenger side glove box area? Maybe I could test some leads in that location?
Am I possibly over thinking this? Bad starter or starter solenoid? I just figured with the codes that came up it would have to be vats system problems.
The TDR can sometimes be at fault. It is located to the right of the glove box, next to the hatch relay. It is pinned to the metal structure of the dashboard. It is easiest to see if you poke your head under the dashboard and look back toward the rear (after removing the lower dash panel).
The TDM[BCM] does not seem to be a common problem. It is located to the right of the radio, pinned to the air bag bracket
As noted in my guide for VATS troubleshooting and info, if you want to bypass the VATS module you need to bypass the TDR and purchase a bypass module for the VATS signal to the computer.
Yes, but that is in a completely different harness. I'm just trying to bypass the relay to eliminate it from being part of my problem. Possibly I jump the two larger yellow wires?
I suggested "If you would like to have specific 93 info, download (free) factory service manual:"
If you download it and look at section 8A-133 you will see some differences between the 1993 and 1995 diagrams.
On page 8A-133-0 the differences are:
The Theft Deterrent Relay is called the "Starter Enable Relay". The sequence of the components in the circuit is reversed - the relay is BEFORE the clutch start switch (or auto transmission position switch).
The wiring for those two components had the colors switched. The Starter Enable Relay has two yellow wires supplying ignition switch "start" position 12 volt power to the relay (same as 95). The signal wire from the TDM is yellow/black (same as 95). BUT the purple wire used in 95 is dark green in 93, and it goes to the clutch or auto trans switch. Then the purple wire runs from the switch to the starter solenoid.
The TDR is the relay in your picture with 2 yellow wires, a green wire, and a black/yellow wire. Connecting the dark green and wither yellow wire will bypass the TDR (starter enable relay).
Thanks for all the help! I was able to bypass the TDR and confirm my clutch switch is good. Car cranks, but still no start. I will have to buy a vats bypass module to get it to start. I did alot of searching on how to install one of those modules and I get conflicting results. Is it installed near the TDM inside the car or by the pcm under the hood? Possibly both? Easiest way would be near the pcm, I would guess. Any detailed instructions with pictures out there?
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