service brake system

[94 eg]

So I put the 8.6" 4.10 rear in tonight and took it for a test drive and on the way back I got a service brake system on my DIC. Just wondering if the axle swap would have anything to do with it. Also the brake and ABS light came on as well.

[djthumper]

Maybe if the PCM isn't reprogrammed with the new gear size.

[94 eg]

Maybe but I thought I would have read about other people having this problem if this is the case. I know there are quite a few who have swaped to a 8.6" and I never read anything about it unless it was a newer TB.

[djthumper]

I am pretty sure I read about it someplace and it may have been an oversite for the articles here. I believe the PCM needs to know the gear sizing to receive the correct data from the sensors for the system.

[The Roadie]

You bled the calipers and the brake fluid level is OK?

I don't know how the 2WD systems knows about gear ratios, or cares. Except for pulses per mile comparison from the rear driveshaft to the pulses coming from the front wheel hubs. Normally, the gear ratio programming is a TCCM item, but it's conceivable the PCM cares, too. I don't think I ever heard of a 2WD owner upgrading to 4.10 rear only. You're the pathfinder. Sometimes that costs a dealer visit to figure out.

[94 eg]

I didnt disconnect my calipers doing the swap and yes my brake fuild is good. Also the TB is 4WD.

[The Roadie]

Sorry, I'm out of ideas. I could have sworn your profile said 2WD when I first looked.

[94 eg]

Update:
I unplugged my brake fuild level switch and went for a short drive and no lights came on. Hopefully its just a bad switch. Just crazy that it started coming on, on my first test drive after the axle swap.

[94 eg]

Well light came back on this morning on the way to work so I guess it didn't get that lucky.

[navigator]

what year 8.6 axle did you use?

[94 eg]

I ordered it for a 2002 but I don't know exactly what year it is.

[Karo]

Hm, never heard of that problem. I could remind that you could install a newer 8.6 axle with a 4 channel abs to a 2002 TB but not a 2002 8.6 rear axle to a newer 2005+ TB.
Here is the Thread from the OS when AlekG had a problem with his 2006 TB in 2008 :http://forums.trailvoy.com/showthread.php?t=44734
Some questions:
1. You have changed the gear ration from 3.42 to 4.10 in the rear axle correct?
2. Have you changed the gears in the front diff?
3. Did you changed the tire size?
4. Have you updated the pcm to new gear ratio and/or tire size?
5. Did you use the same tire manufacturer and tire size on front an rear? (try to change tires from rear to front)

KaRo

[94 eg]

1. Yes I went from a 3.42 to 4.10 on the rear
2. I have a 4.10 front that I hope to get in sometime next week and hope it fixes my problem
3. Yes it has 33" tires
4. No I didn't update my pcm for my tires size But it never through the light before the axle swap
5. Yes on the same tire manufactor and size front and rear.
Thanks for the help guys

[RimoniManu]

I have a 2002 EXT and my brake and abs lights would sometimes come on while driving and other times it wouldn't. From my experience, and I'm not saying I'm right, but bleed bleed bleed. Even when I did my axle swap and put on huge silverado 2500hd calipers, I thought I bled enough, went driving and my lights came on. I bled my brakes more and solved the problem.

[Trail X]

1. Yes I went from a 3.42 to 4.10 on the rear
2. I have a 4.10 front that I hope to get in sometime next week and hope it fixes my problem
3. Yes it has 33" tires
4. No I didn't update my pcm for my tires size But it never through the light before the axle swap
5. Yes on the same tire manufactor and size front and rear.
Thanks for the help guys

I honestly don't see how replacing the front diff would make any difference to the computer. You won't change the ABS signal pulses.

To clarify, is this the ABS light? or a separate service brake system light? I'm betting that the light only comes on after you drive it, right? I am fairly positive that the issue is from the PCM programming of the speed sensors. The sensor on the transfer case output should be off from the front sensors by a certain ratio (the rear diff ratio). That's the only thing I can imagine the issue to be. Has anyone else swapped gears on a 2005-? The issue is moot on a 2006+ because of the rear axle sensors that take the diff ratio out of the equation. To be honest, one of the SAS guys might have a solution for you.

[94 eg]

Still havent had time to put the 4.10 front in.
I have noticed that for some reason the lights only come on every other time I drive the truck.
To JD Yes the ABS light, Brake light, and the DIC says Service Brake System all at the same time.
No you dont have to drive it for it to come on. Sometimes it will light up before I get it out of park, other times I will be 2 miles down the road before it comes on.

[HARDTRAILZ]

Interesting. In all the research I did, of the 2wd and 4x4 axle swaps/gear changes. I never saw this issue. I do know a 2wd Envoy did swap to a 4.10 rear without issue...2002 if I recall. Its on trailvoy.

[Trail X]

Jason, If it is lighting up before you even get it in gear, then I do not think it has anything to do with your gear ratio. I'm suspecting it may be a wheel speed sensor on one of the front hubs. If you can find someone that can read the ABS code for you, that would be immensely helpful.

[94 eg]

Well I finally got around to getting someone to scan it see was was going on. He told me the only thing that was showing up was the speed sensors were not reading the same. He said when the front was reading 3mph the rear was reading 7mph. I don't know what I can do to fix it other than putting the old rear back in, but if thats the case I will just have to live with the light being on. I still haven't got the front diff swapped out yet, hopefully I can this week.

[94 eg]

Found this on the Transfer Case Operations Thread
If the sensors speed on the front hubs don't match the sensor speed on the front output shaft on the tranfer case could this be causing my problem?


Transfer Case Speed Sensors

There are three speed sensors on the automatic transfer case (ATC), two on the rear output shaft and one on the front output shaft. Each speed sensor is a permanent magnet (PM) generator. The PM generator produces a pulsing AC voltage. The AC voltage level and number of pulses increases as speed increases.

Vehicle Speed Sensor

One of the two on the rear output shaft is the vehicle speed sensor (V SS) input to the powertrain control module (PCM). The PCM sends this information to the transfer case shift control module via the Class 2 Serial Data bus.

Rear Propshaft Speed Sensor

The transfer case shift control module converts the pulsating AC voltage from the rear transfer case speed sensor to a rear propshaft speed in RPM to be used for calculations. The rear propshaft speed can be displayed with a scan tool.

Front Propshaft Speed Sensor

The transfer case shift control module converts the pulsating AC voltage from the font transfer case speed sensor to front propshaft speed in RPM to be used for calculations, and to monitor the difference between the front and rear sensor speed. It is also used in the AUTO (Adapt) mode of operation to determine the amount of slip and the percent of torque to apply to the front axle. The front propshaft speed can be displayed with a scan tool.

Service 4WD Indicator Lamp