Location of ABS Sensors on 99 Rodeo 4WD

Had a thread going on 'ABS Light On' but it seems to have died out without my final question being answered. We'd kind of drifted off topic a bit so I thought I would start a new thread. I'm kind of new at this stuff so I apologize in advance if it was the wrong thing to do.

It is my understanding from the research I have done on my 99 4WD that it is supposed to have ABS sensors on each of the four wheels. The 2WD units, on the other hand, have sensors on the each of the front wheels but only a single sensor on the rear -- located on the differential.

My 4WD appears to have the sensor set-up of the 2WD. I was thinking maybe the rear axle might have been changed out but it does have disc brakes on the rear which the 2WD's did not. So why would my truck's ABS be set up like a 2WD?

Anybody have any ideas?

I bought this truck about a month ago. Ironically, I was originally going to buy a 98 LS with 2WD but passed on the deal when I test drove it and the ABS light was on. The dealer said it only needed to have the brakes replaced, which he did, but the light still stayed on. I figured I didn't need ABS problems on top of the other potential problems with these trucks.

A few days later, I ran across this 99 LSE with every option on it. And best of all, the ABS light was off!! Plus, the dealer had just had the fuel pump/sending unit replaced because the gauge had gone out while it was on his lot.

I was immediately in love with the truck. I bought it on Sunday and on the following Saturday the ABS light came on for the first time. RATS!! It went off the next time I started it and I figured it was just a fluke. But since then it comes on much more often and is on all the time now.

I know it's not a big safety issue since the brakes work fine otherwise. I've been driving for 27 years without ABS so I don't 'need' it. It's just that stupid light. It mocks me.

Thanks!

JWS
99 Rodeo LSE 4WD

The only thing that I can think of is that maybe the 98 2wd adn 4wd had 1 sensor, and your truck was one of the frist ones off the line that was called a 99, yet still have the 98 rear ABS setup.

What is the date on the sticker on the drivers side door jam?

-Ryan

That's a plausible explanation that I hadn't really thought of, Ryan. Just ran out and looked on the door pillar -- truck was built in July 99 so wouldn't that make it one of the last 99's built? Maybe they went back to the earlier setup on the 2000's and my truck got the 2000 setup.

Is your '00 Amigo 4WD? If so, what's the sensor set-up on it?

Maybe 2eyefishclaw can shed some light on this issue. Isn't he a tech/mechanic for an Isuzu dealership?

I called Isuzu and the ABS recall has been done on this truck. But maybe the ABS computer is different for the 2WD/3 sensor set-up than for the 4WD/4 sensor system and this is the part of the problem.

Thanks!

JWS

It is my understanding from the research I have done on my 99 4WD that it is supposed to have ABS sensors on each of the four wheels. The 2WD units, on the other hand, have sensors on the each of the front wheels but only a single sensor on the rear -- located on the differential...
As far as I know, the 1998-2004 4x4 & 2wd rodeos have a three channel ABS setup where each front wheel has a speed sensor (thru the backing plates) and the rear has one sensor built into the axle. I just took a quick peek at my 2002 4x4 and the rears do not have individual sensors. There is a wire that appears to go into the top of the pumpkin, I'm guessing that is the rear ABS (wheel speed) sensor. High-end code readers will read ABS codes & tell you where the problem area is. It's usually a dirty or broken front wheel speed sensor, or the infamous 1998-1999 bad ABS pump.
G/luck
Joel

. It's usually a dirty or broken front wheel speed sensor, or the infamous 1998-1999 bad ABS pump.
G/luck
Joel

The infamous bad ABS pump ran continuously when it went bad, right? Mine's not running as far as I can tell. And wouldn't this have been replaced with the ABS recall?

High end code readers doing ABS? Are the ABS codes stored in the ECM? I thought they were in the ABS computer. Local Midas said they couldn't read them; dealer only. Don't really have a problem going to the dealer on this but can't find the time to get there when they are open. Besides, I'd really like to fix this thing at a minimal cost.

And speaking of pumps, computers, sensors, etc., do you know where these things are? The gizmo on the RF of the firewall with all the brakelines coming out of it is the pump, right? The wiring from this thing goes through the firewall to the computer I presume but I don't know where that is.

I had also read that the ABS light could be due to wiring/connector issues but I've looked at all the wiring and connectors that I could find and don't see any obvious corrosion. Could be a wire rubbing inside one of the wire looms, I guess. Any thoughts on this?

I also pulled the front sensor on passenger side -- looked OK. Couldn't get the one on the driver's side out -- lots of rust around it. Afraid to spray too much WD40 around it as I wasn't sure whether it might damage the sensor. PS one came out pretty easy.

Lots of rust under this truck -- it spent the first 70K of its life in the Akron/Cleveland area where they salt the roads heavily in the winter. Whoever owned it before did a good job of keeping the topside looking good but the underneath is kinda ugly.

Thanks for going out and looking under your truck!!!

JWS

I also pulled the front sensor on passenger side -- looked OK. Couldn't get the one on the driver's side out -- lots of rust around it. Afraid to spray too much WD40 around it as I wasn't sure whether it might damage the sensor. PS one came out pretty easy.
JWS

The rust around the connector sounds a little suspicious to me...

Dale

Connector looks fine. It's where the sensor goes through the wheel backplate that is rusty. I could wiggle it a little but couldn't pry it out. Didn't want to break it. I think the sensor might be suspect, especially if it gets a ground of some sort through the sensor body. But it has two wires so maybe there is no gound...

I may try again to pull it out this weekend.

Thanks!

JWS

.... I think the sensor might be suspect, especially if it gets a ground of some sort through the sensor body...
They are usually an optical sensor that reads a toothed ring/gear around the spindle. Rust on the ring, a loose ring, missing teeth, or dirt over the sensor will cause issues. Either way it's a pita to troubleshoot on these trucks. Have to pull the entire hub apart to get the brake rotor off in order to check it out :banghead: .
G/luck
Joel

The front sensors don't appear to be optical but maybe magnetic. When I pulled the one on the passenger side, it had lots of iron filings stuck to it. I wiped them off before re-installing it. Couldn't get the driver's side one out that day and haven't tried again.

The front sensors have pigtails with the connectors mounted such that they point down. They are attached to a metal plate and it looks like the plate is integrated to the pigtail such that it also gets replaced when the sensor is replaced. Anybody know what these are mounted with? I felt around and couldn't feel any bolt or screw heads but maybe they are just covered with dirt?

Also, does anybody know what the resistance measurement on these things is supposed to be?

Thanks
JWS