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Old 02-13-2018, 12:24 PM   #1
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Default Body control module

What exactly does this do? Do 98-02 v6-v8 cars have the same compatible module? I have a 98 car that clicks repeatedly fast under the passenger side dash with battery connected. What other relays are there? On that side or either. Thanks working on a v8 98 roller ....have wrecked 2000ss and v6 car for parts. Where are the screws to remove the dash? I already removed the lower exposed screws. Looking to remove whole dash harness

Mainly seeing if all the 98-02 body control modules are the same and what could cause the quick repeated clicks.

Last edited by 95maroz28; 02-13-2018 at 12:28 PM. Reason: Questions
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Old 02-13-2018, 12:51 PM   #2
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I believe they are responsible for controlling the electronics within the car. I don't know if all the '98-'02 BCM's are compatible as far as plugging them, however if you do swap BCM's you'll need to know that matching key pellet resistance that goes with the BCM. The BCM is a part of the VATS system and it has the resistance value of the key stored in it. You stated that you have a wrecked '00 parts car. If you could use the '00 BCM (if it's compatible with your '98 car) then you'll need to swap out the pellet from the '00 key to the '98 key. Another option is to have your PCM tuned to remove VATS.
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Old 02-13-2018, 05:38 PM   #3
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The BCM handles a number of body related electrical circuits including power locks, keyless entry, courtesy lights, retained accessory power, vehicle anti-theft system (VATS), alarm system, hatch release, and various warning lights and chimes.

There were several different BCMs installed from the factory depending on options but all have been superseded to the same number so basically the same BCM will work in any 97-02 f-body. But if you swap an original one with less options then you will lose those option (e.g. if you had the optional alarm but swap in a BCM from a car that didn't have the alarm then you will lose your alarm).

A new BCM will program itself to the first ignition key used and can never be programmed again. That means a used BCM will only work with the same key resistance value it had in the donor car. If you've got the key from the donor car then that shouldn't be much of a problem... just get a new key cut to match your original but using a key blank that has the same resistance as the donor. Otherwise, you can try doing a VATS bypass using each of the 14 possible resistance values until you find the one that works.

VATS cannot be programmed out. It uses two methods to prevent starting - it disables the starter relay and it disables the fuel enable signal to the PCM. You can program the PCM to ignore the lack of a fuel enable signal but you have to rewire to get around the starter relay being disabled.
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Old 02-13-2018, 09:22 PM   #4
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Thanks the ss has the keychip removed. And the steering column bypass.Plan on converting 2000 ss engine auto trans to m6 98 roller. Will the 2000 harness directly plug in the 2 plugs in kick panel on the 98 m6? Lights work just can't get a instrument cluster reading or trunk to open would just click repetitive fast under passenger dash. What other relays are in dash.

The 2000v6 module is the same as the 98z28. Just don't have the keys for the v6 parts car. So you have to know the vats key value for specific module? Anyway around it or easiest to find value. Does anyone know if 15 resistor bypass kit is for gm 98-02 f-body on eBay? They have a 15 resistor bypass kit for 5$.

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Old 02-13-2018, 11:58 PM   #5
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So If i understand if the wrong key Im just trying to test the bcm it will just kill the starter relay circuit? The body controls will still work, windows trunk latch? I've sat there with security light a few times but never tested out Interior stuff. Or will it cut all power from BCM to PCM? Leaving just a security light.

I have a few f-bodys to work on. Does anyone know where I can find the 15 diff key value for vats. eBay has 2 diff packs of 15 gm vats bypass resistors? Are these the correct ones everyones using. I need the whole set of 15 if that is correct. Thanks let me know. Have couple cars I can do the bypass to if it gives me problems and I also need every possible value to use the keyless BCM.

Last edited by 95maroz28; 02-14-2018 at 12:30 AM. Reason: Vats bypass
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Old 02-14-2018, 09:22 AM   #6
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Thanks the ss has the keychip removed. And the steering column bypass.Plan on converting 2000 ss engine auto trans to m6 98 roller. Will the 2000 harness directly plug in the 2 plugs in kick panel on the 98 m6? Lights work just can't get a instrument cluster reading or trunk to open would just click repetitive fast under passenger dash. What other relays are in dash.

The 2000v6 module is the same as the 98z28. Just don't have the keys for the v6 parts car. So you have to know the vats key value for specific module? Anyway around it or easiest to find value. Does anyone know if 15 resistor bypass kit is for gm 98-02 f-body on eBay? They have a 15 resistor bypass kit for 5$.
The newer harness will probably not work in the 98 car because 98 was a unique year with several differences including a different instrument cluster setup. 99-02 were basically all the same but 98 was different.

GM used the same 15 values for VATS on all their vehicles at the time. Only 14 of the 15 were ever used in f-bodies but I don't remember which one wasn't. Not a problem, it just means that you'll have one extra value to test that wouldn't have been used. Most of the values don't correspond to standard single resistors so you will generally have to use combinations of resistors in series or parallel to get close to each value.

Here is a chart of the values and the standard resistors that can be used to match them. Combinations with + would be connected in series while combinations with || would be connected in parallel. The percentages indicate how close the combinations are to the desired values. VATS allows up to 10% variation.


VATS Resistor Chart
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Old 02-14-2018, 09:33 AM   #7
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So If i understand if the wrong key Im just trying to test the bcm it will just kill the starter relay circuit? The body controls will still work, windows trunk latch? I've sat there with security light a few times but never tested out Interior stuff. Or will it cut all power from BCM to PCM? Leaving just a security light.
Using the wrong key will cause the car not to start because the BCM will disable the starter relay and turn off the fuel enable signal to the PCM. All other functions will still work including lighting, keyless entry, hatch release, etc.
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Old 02-14-2018, 01:12 PM   #8
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Thanks. So you're saying the 2000 ss cluster won't fit in the 98z28? I can't get the miles to read on 98 roller. The wrecked 2000 ss convertible runs and drives great. Are they stored in cluster or pcm. One guy mentioned converting 2000 v6 car to v8 by swapping v8 cluster and the engine pcm harness by two plugs under the right kick panel while keeping original v6 chassis harness. I've seen where this is on the parts v6 car I have. So you're saying I can't do the same by swapping out the wrecked 2000 auto ls1 engine harness/pcm to the good roller 98 m6 harness/pcm by the two plugs under kick panel? As well as cluster from 98v8 not same plug fitment as 2000v8? Will possibly try using the vats bypass and bcm from 2000 ss for testing.
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Old 02-14-2018, 01:47 PM   #9
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The clusters are physically interchangeable but the wiring is different between 98 and the newer models. For example, the 98 has three plugs in the right kick panel where the 99+ models have only two plugs there and the 98 uses a 3-wire temperature sender while newer models have only two wires. Your best bet would be to ensure the harness and cluster are from the same generation (either 98 or 99+) and even then you may have to do some re-pinning of some of the connectors.
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Old 02-14-2018, 09:10 PM   #10
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Does the 98 LS1 auto harness use the same three plugs may just be better to find one of those instead of repining. Will the 98-99+ pcm swap with either/or 98-99+ harness direct plug n play or does harness need correct year/trans. Is the 98 m6 pcm direct fit for 98 auto harness with the 3 Interior plugs to where u can flash it to auto pcm settings. So can you swap 98-99+ pcm or do you need correct harness. They're all f body I hate to repin. I seen eBay sells the harnesses.
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Old 02-15-2018, 08:18 AM   #11
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I'm afraid you're getting into details I don't know. I can tell you that there are multiple different instrument panel wiring harness part numbers based on year, transmission, and options like stereo system and traction control, but not engine type. There are multiple cross body harness numbers based on options like power locks, power mirrors and alarm system where all 99-02 are the same but 98 is different. The engine harness is different for each engine/transmission combination of course but here again 98 is different from 99-02. The PCM itself is different between engines and years (98 is different from 99-02).

Some differences such as stereo type or traction control may have no impact for your needs but others could be significant. The fact that harnesses have different part numbers doesn't necessarily mean they can't be swapped but it indicates that something is different that might make them not interchangeable.
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