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I'm beyond frustrated with this thing and about to pull the drivetrain out for something else. It's a 1997 Z28. LT1/T56. Bought it off a buddy who told me it's reliable but has a few quirks. One of the quirks is that it only runs when it feels like it because of the anti-theft system. I don't have key fobs for it. The VATS resistor has already been done. The battery is new. The car is just absolutely dead except for that stupid alarm. I've been digging around on the internet for DAYS trying to find information but keep getting pointed back to the same dumb things. I saw a video of a guy using a scope on the TDM and he explained that it grounded the starter solenoid while the hot side is switched by the actual switch while going through the neutral safety or clutch switch. He also explained that the fuel side of things uses a pulse and showed the measurements. I bought a gadget off Amazon that was made just for this. When I went to install it my TDM isn't in the location I saw on the video. I read somewhere that it's integrated into the BCM. My BCM is on the passenger side by the blower motor. The instructions for the gadget I bought are non-existent. There are some videos on it but none helpful. Does anyone know how to eliminate this PITA factory security garbage?
Not clear from above statement “The car is just absolutely dead except for that stupid alarm.” But you indicate the engine “….it only runs when it feels like it”. So it starts and runs sometimes?
Since you indicate the resistor bypass has been done, does the starter always crank the engine when the key is turned to “START”? Or is it hit or miss whether it cranks?
If it cranks the engine but the engine doesn’t start because the PCM is not receiving the 50 Hz “fuel enable” signal from the BCM, it should set trouble code P1626 in the PCM. Have you scanned the PCM for codes?
You describe the VATS security system (PASS-Key II), and also refer to an “alarm”. VATS is installed in all 4th Gens. VATS does not include an audible alarm. There is an optional “alarm” system available in 1997. If the car has an alarm, RPO code xxx (have to look that up) would be shown on the Service Parts Identification label in the glove box. I'm not sure if there are overlapping functions between VATS and the alarm. We would have to look that up in the factory service manual. Free download of 1996 factory service manual (should be 99+% identical to 1997).
If the problem is the PCM not receiving the 50 Hz fuel enable system, you need to find the dark blue wire that runs from the BCM to pin A25 on the PCM.
Not clear from above statement “The car is just absolutely dead except for that stupid alarm.” But you indicate the engine “….it only runs when it feels like it”. So it starts and runs sometimes?
Since you indicate the resistor bypass has been done, does the starter always crank the engine when the key is turned to “START”? Or is it hit or miss whether it cranks?
If it cranks the engine but the engine doesn’t start because the PCM is not receiving the 50 Hz “fuel enable” signal from the BCM, it should set trouble code P1626 in the PCM. Have you scanned the PCM for codes?
You describe the VATS security system (PASS-Key II), and also refer to an “alarm”. VATS is installed in all 4th Gens. VATS does not include an audible alarm. There is an optional “alarm” system available in 1997. If the car has an alarm, RPO code xxx (have to look that up) would be shown on the Service Parts Identification label in the glove box. I'm not sure if there are overlapping functions between VATS and the alarm. We would have to look that up in the factory service manual. Free download of 1996 factory service manual (should be 99+% identical to 1997).
If the problem is the PCM not receiving the 50 Hz fuel enable system, you need to find the dark blue wire that runs from the BCM to pin A25 on the PCM.
NOTE: I need to check the RPO code for the alarm, and the dark blue wire PIN number on the PCM. I'LL DO THAT IN THE MORNING.
Injuneer, thank you for the quick response. I understand how the VATS system works. The resistor was in place when I bought the car. As soon as I open the door the lights flash and the horn blares if it's hooked up. It doesn't crank and has no power anywhere BUT the functions controlled by th alarm. I'm gonna hop on Identifix an print some wiring diagram when I get to the shop today so I have more ammo.
The PASS-Key II and Universal Theft Deterrent systems are shown starting on page 8A-133-0 in Service Manual Volume 2.
The optional theft deterrent system is RPO code "UA6". See if that code is shown on the Service Parts Identification label in the glove box. The wiring diagram on page 8A-133-2 shows the added components for UA6 option, including the parking lam relay, theft deterrent shock sensor, security indicator LED. The connection to the horn relay from the BCM is not shown with the UA6 designation, so it may indicate the horn is part of both the base PASS-Key II system and UA6. I do not know if the the horn was integrated with the PASS-Key system, or only with the UA6 option. The 93-95 PASS-Key only system does not have a connection to the horn. The horn wiring diagram shown on page 8A-40-0 indicates the connection from the BCM to the load side of the horn relay only with UA6.
The dark blue wire for the fuel enable signal connects to the PCM starts at the BCM as dark blue, but it goes through connector C230 where it changes to dark green (ONLY SHOWN IN 133 SECTION - ON PCM PINOUTS SHOWN AS "BLUE") and to the PCM on Connector 1, Pin 25. IF THAT'S AN ERROR IN THE 1996 MANUAL, THE 1997 MAY CORRECT IT, BUT I DON'T HAVE ACCESS TO THE 1997 MANUAL. SCHEMATIC ON PAGE 6E-457 SHOWS THE ENTIRE 229 CIRCUIT WIRING AS DARK BLUE.
OP, your problem is that you don't have a wireless key fob to disarm the alarm. The alarm is setup to arm when you press the lock switch on the doors or press the lock button on the key fob. From the factory the alarm is setup in Mode 3. Even if you have the correct door key and unlock the door with that key, the alarm will go off unless you put the correct resistance key in the ignition and start the car within about 10-15 seconds of unlocking the door. However if you have screwed around with VATS and the system does not see the correct resistance key, it most likely will still go off after you try to start the car.
The owners manual describes the procedure to on how to change the mode of the alarm...which does include Mode 1 which will disable the alarm system. Starting on page 2-18, this will tell you how to do that. Page 2-20/2-21 describes the modes for how the car reacts when the alarm is armed. Page 2-21 describes the alarm modes(Mode 1 will disable the alarm from arming).
There is one more thing that might screw you over....in order to change the alarm mode, the system may need to see the correct resistance VATS key. So keep that in mind if you have altered your VATS.
If the above is the case you can try this.....if you manually lock the doors with your fingers and not the door lock switch, the alarm will not arm in Mode 3 if I recall correctly.
My advice to you is to get a wireless key fob off ebay or from some other source, program it to the car, and keep the alarm functional. It may save your car from being stolen. But...this may also hinge on VATS seeing the correct resistance key to add a new wireless key fob.
09-26-2024, 06:28 PM
