ABS Problem 98 T5 Topic is solved

[mecheng]

Problem: ABS light is on most of the time. With winter approaching, I'd like to fix it.

Checked the front ABS sensors, they measured 1080 ohms so they are okay.
I could not find the connector for the rear sensors, I guess they are above the gas tank?
Or should I check the resistance at the ABS connector, I do know which pins correspond to which sensors from my wiring diagram.

The PO said he changed the ABS computer, but I'm not sure if his mechanic just pulled something from the junk yard.

Occasionally, the ABS light is off, but after a while of driving, I heard a buzz, for a couple of seconds and then the ABS light illuminates. My friend works at a dealer and it scanned RF and RR sensor even though I confirmed the RF sensor is okay.

any input is appreciated

[FLXC90]

Try checking the rear wheel sensors at the plug underhood. If the sensors ohm good at the connector, try the clean and reseat process a couple times, maybe some dielectric grease. maybe a corroded, or just loose connector? After that maybe check/clean reluctor wheels. Any other symptoms of a flaky ignition switch?

[phils94850]

On my 96 I had two problems.. The pass rear ABS sensor wiring was worn and I had to open up the ABS module and re-solder.

[mecheng]

Ok I will check resistance at module. Does the connector unplug easily?

[phils94850]

To check the sensors you do it at the ABS module connection under the hood. If it shows to have a bad one, the rear, you have to replace both sensors at once ( its made that way, two sensors one harness ) and the wiring goes up between the fuel tank and into the trunk where the fuel pump access cover is.

[mecheng]

I checked all 4 sensors on my s70 and they all read 1000 ohms.


On my 850, the RR sensor read infinity, is the sensor bad or wiring?
The abs module for the 850 was repaired by Midwest a few years ago.

[Matty Moo]

Bad wiring if you're reading OL through the harness. The sensor won't test as open unless it is smashed to bits.

Also, you want to check through the harness where it actually connects to the module. That way you are testing the entire circuit. Wiring going bad happens more often than people think while actual sensors rarely go bad.

[mecheng]

UPDATE:

S70
Good news on the S70, removing the harness connector (pump and computer), cleaning it with some brake clean (ran out of contact cleaner) and spraying a very light coat of lithium grease on the pins: reseated it and drove it today. Light dissapeared after a couple of minutes and STAYED off.
Did a few emergency stops in the ran and the abs kicked in.... ahh nothing like a foot massage.
The pins were not dirty, but maybe it wasn't seated properly or some oxidization. The connection doesn't feel like the most robust. Folks, moral of story is: check your connector first and sensors from the connector

850
Matty or anyone else. I checked the resistance between pin 17 & 1 at the harness connector to the ABS ecu which is the RR sensor and it is open. I can't see where the rear ABS sensor connects to the wiring, do I have to drop the gas tank? Why did Volvo not make the rear ABS sensor connector simple like the front?

[phils94850]

As I mentioned.. on the 850 the connector is where the fuel pump cover is in the trunk. I had to drop my tank a little to get clearance to run the new abs sensor wiring up to it. Mine showed the RR as well and it ended up being the harness had rubbed through on the frame and also the ABS module needed re-solder.

[mecheng]

Ok, I will do a check. Did you cut the existing wire out and solder in a new wire or just replace the entire rear sensor assembly. What does the connector look like, I assume four wire?

If you tie a piece of string to the old wire when you pull from underneth I don't think you need to drop the gas tank (in theory).