85-86 ABS issue
Thread Starter
Burning Brakes
Joined: Apr 2010
Posts: 863
Likes: 63
From: The Netherlands
85-86 ABS issue
Hi guys,
After solving my broken MAF issue, I took the car out for a (very pleasant :-)) drive.
Car was absolutely fine, zero issues.
After about 100 miles I was greeted by the "Antilock" warning light.
It comes on as soon as the car starts moving forward (when starting and reversing it stays off).
I suspected the ABS sensors, so I decided to measure them at the ABS control unit. Unfortunately I did not find an immediate "smoking gun". The front sensors both measure around 1600 ohm, and the rears are both at around 1000 ohms..
Who can tell me what to do next? I dont have an occiloscope to measure the signal, any pointers on what to check next would be highly appreciated!
Many thanks!
After solving my broken MAF issue, I took the car out for a (very pleasant :-)) drive.
Car was absolutely fine, zero issues.
After about 100 miles I was greeted by the "Antilock" warning light.
It comes on as soon as the car starts moving forward (when starting and reversing it stays off).
I suspected the ABS sensors, so I decided to measure them at the ABS control unit. Unfortunately I did not find an immediate "smoking gun". The front sensors both measure around 1600 ohm, and the rears are both at around 1000 ohms..
Who can tell me what to do next? I dont have an occiloscope to measure the signal, any pointers on what to check next would be highly appreciated!
Many thanks!
Team Owner
Joined: May 2004
Posts: 31,181
Likes: 4,175
From: Philly PA
if thats what you are reporting ,
then you need to check the wiring at the connectors under the hood and at the wheels,
and the grounds at the wheels and the spare tire well,
Remove the sensors and clean off the dirt ,
put DC111 on the sensors to stop them from corroding.
then you need to check the wiring at the connectors under the hood and at the wheels,
and the grounds at the wheels and the spare tire well,
Remove the sensors and clean off the dirt ,
put DC111 on the sensors to stop them from corroding.
Thread Starter
Burning Brakes
Joined: Apr 2010
Posts: 863
Likes: 63
From: The Netherlands
I did another check today, and put the multimeter to AC.
When driving around 50 km/h the front sensors produce about 5 volts AC (left slightly more than right), the rears produce about 2 volts at that speed, also left and right equal.
So it seems the sensors are reading, corroded wiring under the hood seems very unlikely since the wires are practically new, the car never sees any rain.
Any other things I can check before tearing down stuff?
thanks
When driving around 50 km/h the front sensors produce about 5 volts AC (left slightly more than right), the rears produce about 2 volts at that speed, also left and right equal.
So it seems the sensors are reading, corroded wiring under the hood seems very unlikely since the wires are practically new, the car never sees any rain.
Any other things I can check before tearing down stuff?
thanks
Rennlist Member
Joined: Jun 2005
Posts: 10,574
Likes: 1,027
From: Oman
Remove the ABS sensors, clean them up and the receptacle they sit in. On mine I found a pile of crap. Each sensor on my ABS tested at 1000 ohms.
I also knew those bullet connectors were falling apart so I decided to try and disconnect all 8 of them - the plastic disintegrated on all of them. The bullet connectors inside were fine - I disconnected and remade every one of them several times and one failed so I had to remake that connector pin. I fitted a heat shrink sleeve over every connector joint and some heat shrink over the job lot.
On my model one also has to contend with the brake pad warning and the RDK system cables- I use neither of those two systems so no issue with them.
I also knew those bullet connectors were falling apart so I decided to try and disconnect all 8 of them - the plastic disintegrated on all of them. The bullet connectors inside were fine - I disconnected and remade every one of them several times and one failed so I had to remake that connector pin. I fitted a heat shrink sleeve over every connector joint and some heat shrink over the job lot.
On my model one also has to contend with the brake pad warning and the RDK system cables- I use neither of those two systems so no issue with them.
Rennlist Member
Joined: Apr 2007
Posts: 1,971
Likes: 181
The main ABS ground under the hood near the power steering reservoir should be cleaned, and I think you implied that you have already done this. While youre concentrating on this system, check the ABS wiring looms that run over the rear trans-axle. The fasteners that secure them over the transaxle give way and the looms can hang into the half shafts and get beat up, while the car is in motion.
Thread Starter
Burning Brakes
Joined: Apr 2010
Posts: 863
Likes: 63
From: The Netherlands
Quick update: I bought a cheap oscilloscope from Amazon, it should arrive today. Will check the signal at the ECU to narrow down where the issue is coming from, before touching the brittle ABS harnesses.
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Burning Brakes
Joined: Mar 2018
Posts: 909
Likes: 368
Good idea to scope it out. There are two more tests you can / should do.
1. You also need to ensure none of the eight ABS sensor wires have any continuity to ground. So access the harness plug and test for continuity between each of the 8 sensor wires and a chassis ground. There should be none. It is possible for the sensor wires to have the correct continuity across the 2 pins while one of them is shorted to ground. This is quite common on these older ABS sensors as they can get damage internally and then the signal can find a path to ground by way of their metal cases.
2. The ABS ECM tries to test or exercise the Hydro Unit pump motor for a few seconds at about 3 to 5 MPH. If this test fails you will get an ABS lamp. You can apply +12v to pin 26 and that should trigger the ABS pump motor. If it doesnt you will need to figure out why. You can apply +12 to the pump motor itself (ensure the ABS ECM is still disconnected) to hear it run. You can also apply a test light to the curcuit to see what the pump motor is seeing. You also will need to check the relay on top of the pump motor and the other relay in the central electrical panel to ensure they are doing relay stuff as designed.
Last edited by icsamerica; Today at 11:17 AM.
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Burning Brakes
Joined: Mar 2018
Posts: 909
Likes: 368