Hi All,
1.9JTD 8v.

Anyone any ideas why Front left rpm sensor ( new hub , bearing and sensor) - not installed in knuckle when plugged in clears the ABS warning light, but when installed in the knuckle the warning light comes back on. :bang:


Both new and old sensor , when multimeter is used , to check sensor,shows an open circuit. This is the 3rd hub fitted in so many years, all being replaced due to ABS stating no signal from left front wheel sensor.


The wiring from sensor plug to ABS ECU pins 19 & 20 seems to show full continuity.

Thanks for any assistance in advance.

Does the sensor read the bearing, or a separate reluctor ring? The bearing will have the magnetic sensor ring on one end only, and if fitted in the wrong way, the sensor and ring will be at opposite ends. Despite this being a known problem for many years now, it still happens.

Do not fit the sensor using copper anti-seize, as this has been know to interfere with the sensing.

Thanks for the tip.
The sensor is built in to the hub. it has a black plastic ring with a wire from the back side of the hub, where you push the drive shaft through.

I could have sworn that before dismantling the knuckle and removing the hub, I disconnected the ABS connector, and plugged in the new ABS connector with the hub in my hand. I turned on the ignition and no ABS light was showing on the dash.

I installed the new hub, and now the ABS light is back on.

I put a multimeter onto the new sensor but cannot get it to show a resistance. ( I didnt check before hand to see if it read a resistance.)

I have unplugged the front right sensor and this does not have resistance either, So not sure if they should have a resistance if good.
Multiscan confirms that the ABS fault, is still only on the front left ( the new ABS and hub bearing).

I've looked at the parts listing and see that the hub is a complete unit, so the bearings should not be in the wrong way.

There are two types of sensor in general use, some show a resistance, the others don't, so as long as both are the same, that means nothing.

I see that there were two different sensors used, but of course there is no detail as to the differences. Check that the new one is exactly the same dimensions as the old one, as proximity to the bearing is important.

Swap the sensors left to right, see if the fault moves across the car. If it does, sensor is at fault, if it does not move, either the wiring or the bearing is at fault.
Having said that, just looked at Mister Auto and it appears that the sensor is built into the hub, so is part of the new bearing/hub. Perhaps the Fiat parts listing is for the wiring only?

When the ignition is turned on, the ABS light should illuminate for about 4 seconds, while the self-test runs through. If all seems well, the light goes out. Then as you move, it compares signals from all four wheels and puts the light on again if not happy. If the light is on before the hub turns, it is not happy with the self-test

With MES, you should be able to get a speed reading from each wheel if spun. Might be a useful test. If you are saying that it works with the hub held in your hand, but not once fitted into the strut, you need to look carefully at its fitment, to check for the sensor fouling. The hub mounts to the strut with three bolts, does that mean three possible fitting positions? Does it need moving around one?

The Hub is Part # 51748680, The ABS sensor is an integral part of the hub unit. So I would have to swap the hubs over from left to right and visa versa to swap the sensor.



The red bit is the location of the ABS sensor wire and connector as installed in the steering knuckle. ( Same as original location and as the right hand side)

The ABS light stays on after the self test, and MES says no signal from left front.( the new ABS side).

With the hub removed from the knuckle and plugged in the ABS light is still on. ( Check for fouling on installation)

I am pretty sure that before installing for the first time into the knuckle the new Hub when plugged in extinguished the ABS light after the self test.
I am now questioning myself whether that this was the case..

BTW. The reason I am changing the the Hub is because I noticed the previous hubs ABS wire was damaged due to the wire rubbing on the driveshaft. I repaired the wire but still the ABS light was on, hence the new hub.

Next step is to check the loom again for continuity between sensor and ABS ECU.

Re: SOLVED - ABS Sensor Issue

The issue has been diagnosed as a break in one of the wires from the middle connection cable between the sensor connector and the ecu connector.

The run of the cable when installed has a bend in it, and when bent the inner cable was stretched and both halves of the inner wire were not in contact.

However when the cable was unplugged and tested the cable was straighter and made a connection between the 2 halves.


Joining the two halves with a inline connector, restores the continuity when installed on the vehicle.:slayer:

Thanks again for your suggeestions for diagnosis Bill.