VATS Bypass Tutorial with Pics

[yellowlust]

Have you ever had that sickening feeling of turning the key and nothing happening, not even the gnashing sound of the starter? Welcome to the wonderful world of VATS.

I've now had my 86 (now departed) and 95 both strand me in such a manner.

There are quite a few posts about VATS, but I'm going to try to provide a picture guide for those of us (like me) who are not entirely electrically-savvy. Information was gathered from this forum and from an email from jmccloud.

Troubleshooting included pulling the clutch safety switch out and testing. Also trying to clean the ignition switch and key pellets. And then finally, sticking the key in and seeing if i could see any resistance in the wiring harness. More details on this below.

Step one: Get your multimeter (mine was something like $5 at Harbor Freight) and figure out your key pellet resistance. Mine happened to be 526 ohms. I didn't know how to read my multimeter very well so the first time I went to Radio Shack I got 10k ohm resistors.

Step two: Use this chart to figure out which resistor set you are in. I am in #2.

#
Nominal
Low
High

#1
402
386
438

#2
523
502
564

#3
681
654
728

#4
887
852
942

#5
1130
1085
1195

#6
1470
1411
1549

#7
1870
1795
1965

#8
2370
2275
2485

#9
3010
2890
3150

#10
3740
3590
3910

#11
4750
4560
4960

#12
6040
5798
6302

#13
7500
7200
7820

#14
9530
9149
9931

#15
11800
11328
12292

Step 3: Go to Radio Shack and get some resistors. At $.99 for 5 you can afford to get a bunch if you need to.

I knew from the chart above that I needed to get to something in between 502-564 ohms. So using the info in Step 4 I got some 220 and 330 and then some 10 ohm, just in case. I lucked out, as not all combinations will be that easy.

Step 4. (from jmccloud)
Combine resistors until your multimeter gives the same reading for the resistors as it does for the pellet in the key. Resistors typically have a 10% tolerance on value so you may have to try several different ones of the same rated value to get what you want.
Resistors connected end to end 'add' value. So two 1000 ohm resistors connected end to end would measure 2000 ohms. That's a 'series' connection.
Resistors connected side to side in a 'parallel' connection combine according to the formula A*B/(A+B). So two 1000 ohm resistors connected in parallel would be 1000*1000/(1000+1000) or 1000000/2000=500ohms. Or a 1000 connected in parallel to a 500 would be 1000*500/(1000+500) or 500000/1500=333ohms.
So use several resistors in series or parallel or a combination and you can get the "Nominal" value very accurately.

Step 5: Find the VATS wires. This info is for a 95. Yours may be different.

The white wires with the orange cover are the wires coming from the ignition switch. For trouble shooting I hooked up the multimeter and put the key in the ignition. I got no change on the multimeter.

These are the wires that connect from the wires coming from the ignition switch and go to the VATS box or whatever you want to call that evil thing. That big clump of relays are left over from an aftermarket security system a previous owner had installed. One these days I'm going to rip that @#%% thing out.

Step 6: Testing. I prefer testing as i go along. I'm funny that way. Maybe it's from hanging upside down under the dash for too long.

I took my two resistors (220 and 330) which I had soldered (poorly) together and hooked up alligator clips to the wires going to the VATS box. (At this point we don't care about the wires coming from the ignition switch.)

And the car started for the first time in a week. Phew.

Step 7. Cleaning up the installation. Now I was faced with figuring out how to install the resistors permanently. The connector going to the VATS box was a male and I didn't have a good way to attach the resistors. So I removed the connector cover and soldered the resistors right to the male ends. Hopefully when I restore this car in 20 years I'm able to reverse this.

I covered it with heat shrink tubing and tucked everything carefully up under the dash.

And then I went for a drive.

Total cost:

Tow home: $50
Resistors: $4
Chiropractor visit from cramming under the dash: $7000
Joy of defeating another GM engineer: Priceless

 

[jmccloud]

VATS

NICE WRITE-UP!!!!

and thanks for the credits


I don't copy and paste much stuff from forums, but this one's on my hard drive. Good job.

 

[Ghost~3~]

Well "HOT" DAMN!! That "INTERMITTANT" NO START has been driving me "MAD" for almost a YEAR or More, and I've replace about ALL ya can replace and it STILL left me stranded!! ad

Headin off to Radio Shack PRONTO!!!

 

[Key West Jack]

Man, well done. Thank you!!!

 

[g-force junky]

as a side note if you measure the voltage coming from the vats module it will read 5v dc. if no voltage is present the addition of resistor's in place of the key will have no effect on a non start condition. then the module is at fault.

 

[stearnman]

Yellow, nice writeup. What I would do to clean things up some, would be to go back to Radio Shack...get a small project soilder board and a small project box to fit. Either add some type of connectors to you new "VATS resistor box" or just directly run the wires in and soilder them to the board as well. Clean and safe.

 

[yellowlust]

Yellow, nice writeup. What I would do to clean things up some, would be to go back to Radio Shack...get a small project soilder board and a small project box to fit. Either add some type of connectors to you new "VATS resistor box" or just directly run the wires in and soilder them to the board as well. Clean and safe.

Actually what I will do is take the VATS bypass I bought for my 86 (but never used as it's problems were more of the 'dirty ign lock-kind') and take it apart and put the different resistors in it.

That item is a connector that fits the wiring harness and the other end is just some bigger connector that houses the resistors, then filled with epoxy.

I'll post pics if I ever get around to it.

Or does anyone know where to get the specific connectors for the GM Harness?

 

[Drjohn]

I've apparently already got a bypass. My key has no pellet.

I still get an intermittent no start however.

 

[Fast Freddie]

VATS bypass idea.

when you're out stomping around your favorite junkyard, cut a few VATS connectors ( steering wheel end ) off any car that has VATS and solder your resistors to the cut off connector. then you can just plug the connector/resistor pigtail assembly into your cars harness.

View attachment 14610

 

[speedmaster4]

vats final answer

for under $10 of raddyshack parts, you can build a 30 hZ generator that tells the ecm ''all is cool'', ok to pulse injectors:

then bypass the starter relay with a ''trailer wiring connector''.

foget vats ever existed.

 

[Fast Freddie]

sounds interesting.......... got details?

 

[speedmaster4]

sounds interesting.......... got details?

ecm outputs +5v and must see this output ''grounded'' at 30 hz (continuous ground will not work) before the ecm will ''pulse'' the fuel injectors...you can eliminate the ign key resistor, vats module, assoc wiring by sinking (grounding) the ecm output (86-89 ecm pin B6, white wire, other years vary) into a simple 30 hZ gen.

i used the ''venerable'' 555 ic chip with resistors, capacitors to do it (plus a transistor to sink, as the 555 supposedly can sink directly but i haven't figured that out yet)and diodes to assure no backfeed/damage to the ecm...my concoction has three wires leaving it, which tie into existing wires at the ecm for +12v/ground/ vats +5v output.

was into solid state design long ago, still newb with internet, can't scan /post the schematic...last time i said ''freebie'' on the net i got 2000+ requests, never again(you do the math)...for a minimal donation (very minimal,whatever you think correct, i have no desire to make a profit and then need to deal with the feds re taxes) to cover gas/photocopy/ mailing i will be happy to send you the schematic/raddyshack parts list to do with as you please --post here, mfg,etc.

there was an on-line vendor (still ?) that sold the device, apparently also 555 based, but in a plastic housing with a red LED (oh wow) for abt $50, if you're not into making a little solder smoke...i can't recommend them as i never bought one,tho.

btw, you can check if the ecm/ vats output is properly conditioned by checking voltage on that wire from ecm pin B6 with a digital VOM, abt +2.5 volts means go, 0 or +5v will result in a ''no injector signal'' at the ecm/injector pins.

 

[TedC]

Adding a resistor is a great idea if the issue you are having is in the cylinder key contacts. This bypass still depends on a working VATS relay. Took me some 2+ hours to replace because it is well hidden in the center dash. Speedmaster4's idea in fooling the ECM sounds like the best "true" bypass to all the VATS components that can cause a no start condition.

 

[badabing9]

Have you ever had that sickening feeling of turning the key and nothing happening, not even the gnashing sound of the starter? Welcome to the wonderful world of VATS.

I've now had my 86 (now departed) and 95 both strand me in such a manner.

There are quite a few posts about VATS, but I'm going to try to provide a picture guide for those of us (like me) who are not entirely electrically-savvy. Information was gathered from this forum and from an email from jmccloud.

Troubleshooting included pulling the clutch safety switch out and testing. Also trying to clean the ignition switch and key pellets. And then finally, sticking the key in and seeing if i could see any resistance in the wiring harness. More details on this below.

Step one: Get your multimeter (mine was something like $5 at Harbor Freight) and figure out your key pellet resistance. Mine happened to be 526 ohms. I didn't know how to read my multimeter very well so the first time I went to Radio Shack I got 10k ohm resistors.

Step two: Use this chart to figure out which resistor set you are in. I am in #2.

#
Nominal
Low
High

#1
402
386
438

#2
523
502
564

#3
681
654
728

#4
887
852
942

#5
1130
1085
1195

#6
1470
1411
1549

#7
1870
1795
1965

#8
2370
2275
2485

#9
3010
2890
3150

#10
3740
3590
3910

#11
4750
4560
4960

#12
6040
5798
6302

#13
7500
7200
7820

#14
9530
9149
9931

#15
11800
11328
12292

Step 3: Go to Radio Shack and get some resistors. At $.99 for 5 you can afford to get a bunch if you need to.

I knew from the chart above that I needed to get to something in between 502-564 ohms. So using the info in Step 4 I got some 220 and 330 and then some 10 ohm, just in case. I lucked out, as not all combinations will be that easy.

Step 4. (from jmccloud)
Combine resistors until your multimeter gives the same reading for the resistors as it does for the pellet in the key. Resistors typically have a 10% tolerance on value so you may have to try several different ones of the same rated value to get what you want.
Resistors connected end to end 'add' value. So two 1000 ohm resistors connected end to end would measure 2000 ohms. That's a 'series' connection.
Resistors connected side to side in a 'parallel' connection combine according to the formula A*B/(A+B). So two 1000 ohm resistors connected in parallel would be 1000*1000/(1000+1000) or 1000000/2000=500ohms. Or a 1000 connected in parallel to a 500 would be 1000*500/(1000+500) or 500000/1500=333ohms.
So use several resistors in series or parallel or a combination and you can get the "Nominal" value very accurately.

Step 5: Find the VATS wires. This info is for a 95. Yours may be different.

The white wires with the orange cover are the wires coming from the ignition switch. For trouble shooting I hooked up the multimeter and put the key in the ignition. I got no change on the multimeter.

These are the wires that connect from the wires coming from the ignition switch and go to the VATS box or whatever you want to call that evil thing. That big clump of relays are left over from an aftermarket security system a previous owner had installed. One these days I'm going to rip that @#%% thing out.

Step 6: Testing. I prefer testing as i go along. I'm funny that way. Maybe it's from hanging upside down under the dash for too long.

I took my two resistors (220 and 330) which I had soldered (poorly) together and hooked up alligator clips to the wires going to the VATS box. (At this point we don't care about the wires coming from the ignition switch.)

And the car started for the first time in a week. Phew.

Step 7. Cleaning up the installation. Now I was faced with figuring out how to install the resistors permanently. The connector going to the VATS box was a male and I didn't have a good way to attach the resistors. So I removed the connector cover and soldered the resistors right to the male ends. Hopefully when I restore this car in 20 years I'm able to reverse this.

I covered it with heat shrink tubing and tucked everything carefully up under the dash.

And then I went for a drive.

Total cost:

Tow home: $50
Resistors: $4
Chiropractor visit from cramming under the dash: $7000
Joy of defeating another GM engineer: Priceless

i did this years ago and works well. i placed a switch in a smal box and in one position had it in the "vats on" position for unfamiliar neighborhoods and "vats off" for more familiar surroundings. then, just hid the box....

 

[91 corvette]

I got a vats bypass from ecklers for 25or30 bucks and ended my vats problem for good. Drive on.

 

[wrenchmantee]

My VATS drove me crazy too long...I beat it on my own terms! First go to TBI power chips and get a reflashed memcal prom, Deleting the VATS program (cost about $75.00) this does away with the fuel pump and injector pulse problem. Then drop the driver column cover and find the relay with the large yellow wire and the large purple wire, cut them at the relay and butt connect the two of them together. That takes care of the starter interrupter relay problem! Then throw away the remote control and lock your doors when you want! CAVEMAN STYLE....

 

[Surfin' Elvis]

VATS or not?

No click from solenoid on start.
Starts fine with starter relay jumped (purple wire to big yellow wire) and relay removed.
Resistance in key pellet matches resistance (approx. 887 ohms) at ignition side of two-prong connector under dash when key is inserted in cylinder.
I was advised on another forum that my issue is with the wiring harness on the steering column. I was convinced it was the CCM.
Is there any test I can perform to determine where my problem lies?

 

[TedC]

I'm amazed at the misleading information in this post. If we define a VATS bypass as adding a resistor, then don't assume this will correct ALL VATS related issues. If the issue you have is related to poor contacts with the resistor on the ignition key, then this bypass will work. However, I have worked on several C4s that this was NOT the part of the VATS system that failed.
Surfin' Elvis, I would suggest using a GM service manual to pinpoint the issue. I have found on three C4s, including my 1988, that the the VATS relay was the source of the no start condition. I verified that this relay was being energized by the VATS computer, but dead on the output to the starter relay. A resistor bypass will NOT solve this issue.

 

[Surfin' Elvis]

Thanks, TedC.
I have used my year-specific GM service manual to perform every diagnostic test for this no-start condition. The result of my three 12-hour days has been the same no-start condition.
This VATS module, a phrase tossed around here as if it were common knowledge, does not exist in my service manual. I assume we are talking about the CCM located behind the stereo head unit? If not, where is this module?
My 94 starts fine with the starter relay removed and connection jumped.
I need some help tracking down the problem.

 

[TedC]

Surfin' Elvis, What does CCM stand for? I'm referring to the VATS module (computer) and VATS relay that has a complete service section in the GM service manual. In 1993 the keyless transmitter was introduced, and maybe the VATS module was replaced with the CCM??? Using the service manual, can you trace to the device that uses the ohm value as input? I would suspect that this device enables the rest of the system to receive voltage if the value is correct.