[945 TDi] I'm trying to make sense of an ABS/Speedo issue.

[ApacheTech]

I've read a number of posts on here from people with similar issues with various cars, but all the talk goes way over my head.

Last week, the ABS warning light came on, on my dashboard, the speedometer stopped working, and the mileage isn't going up. I need someone to walk me through this, as is explaining it to a five year old, who only know that the car is blue (even though, officially, it's supposedly green!).

I have taken some pics of the sensor on the rear axle, the connectors in the real wheel arch compartment... and some other sensor connectors, under the bonnet, at the front. I need to drive a few hundred miles in August; I'm heading away next Thursday, and I'm in work most of the time until then; so I need to get this fixed.

What is what... what needs fixing... and how do I know what parts to buy? The last time, with the glow plugs I needed to get, I got the wrong type, and they took nearly a month to arrive. I can't do that again.

https://imgur.com/a/60ctN6v

The pics are too big to upload to here.

[J liddy]

Hello think I remember your glow plug issue .they are really not hard to get you were unlucky and been given wrong advice .
The ABS issue if it was front wheels is not that bad a job I did mine I used the fault finder under the bonnet on right hand wheel arch tower .are you familiar with this that's my 1st step

[360beast]

I would say it is the speed sensor or more likely rotten wiring to the sensor on the rear axle but it would be best to read the codes using the code reader under the bonnet like Jim says to get a clearer picture of the fault.

Guide here

https://www.volvoclub.org.uk/faq/EngineOBDCodes.html

I would thoroughly inspect the wiring (you may need to cut the insulation) because it goes black, hard and brittle. This is much more common than the sensor failing, I have had no personal experience of the sensors failing but that's not to say it doesn't happen. The worst one I had was where I had to replace the wiring loom from the sensor right back in to the boot compartment because it was that corroded.

The Speedo sensors are now being remade by Volvo so you can order one from FRF Volvo in Swansea or any dealership but FRF are very good.

1398321 is the Volvo part number.

It could also be (but less likely) the ABS ECU but check the wiring to the sensor first, check the abs fuse is plugged in properly and remove the black cover over the ABS unit in the engine bay and check the fuse there but they shouldn't stop the Speedo from working.

[Forrest]

You need to keep your mind open to the possible cause of your problem and work through fault-finding logically.

It could be one or more sensors, wiring or a problem with the instrument cluster itself.

If your car has the diagnostic probe mentioned above then use it to read the ABS fault codes.

https://www.volvoclub.org.uk/faq/Bra...cCodeRetrieval

If there is a code stored for the rear sensor then there is a good chance either the wiring or the sensor is the cause. The front sensors will not affect the speedo.

If you confirm a rear sensor fault then the simplest thing to check first is the physical integrity of the cabling and any connectors in it. Trace it back from the sensor. Faults are usually near that end. Try pulling apart connectors and cleaning the terminals. But be careful, they are likely to be fragile.

I am fairly certain the rear speed sensor is a two wire circuit. That connector you have found in the luggage area looks more like the fuel pump and gauge wiring.

As a last resort consider changing out the actual sensor. It will be fragile, the screw is likely rusted in and replacements are expensive and hard to come by as they have been out of production for a while.

Be aware that Volvo instrument clusters are renowned for failures too. The symptoms you have described are unlikely to be down to the cluster - simultaneous ABS light and inoperative speedometer. However, it is not impossible particularly if you have had any water ingress or been doing work in that vicinity before.

You do not want to go to the trouble and expense of replacing the rear sensor only to discover down the line that you have actually got a faulty front sensor plus a common cluster PCB fault occurring concurrently.

Good luck!

[jpliddy]

if by chance the speedo in the dash has failed i have one here for you ,but i have a complete dash unit to test on your car too , that shoud get to the bottom of your problem ,i have done the fault code test to find the problem with my ABS sensor too you may want to pop over to me at newcastle under lyme ,only a thought

[jpliddy]

O i also have a spare ABS sensor to test on the car here too

[Laird Scooby]

From your description, it's either the sensor on the back axle or the wiring to it, just like Luke said further up.

You likely won't get any fault codes except perhaps on the ABS part, assuming your car is post 92 and has the Bosch ABS-2E system. If so, it'll say the "rear ABS sensor is faulty, open or short circuit or wiring defective" i believe is the exact words.

Before 1992, the Bosch ABS system was used which had no fault code capability.

The rear ABS sensor feeds not only the ABS ECU (sited above the injection ECU in the drivers kick panel area) but also the instrument cluster.

[ApacheTech]

Originally Posted by Laird Scooby

From your description, it's either the sensor on the back axle or the wiring to it, just like Luke said further up.

You likely won't get any fault codes except perhaps on the ABS part, assuming your car is post 92 and has the Bosch ABS-2E system. If so, it'll say the "rear ABS sensor is faulty, open or short circuit or wiring defective" i believe is the exact words.

Before 1992, the Bosch ABS system was used which had no fault code capability.

The rear ABS sensor feeds not only the ABS ECU (sited above the injection ECU in the drivers kick panel area) but also the instrument cluster.

This went waaaaay over my head. I know that the car is blue. Regardless of the fact the documentation says green. Me and my dad always see it as blue, my mum and my sister always see it as green. I still think the paperwork is wrong. That's as far as my knowledge of it all goes.

[lynns hubby]

Pic 7 with the connector opened up looks like a starting point. Assuming its not a "Trick" of the camera, If you look at the top and bottom Right hand side spades (connectors) they look to me to have corroded as they are a blue/green colour. I would start by cleaning them up first.

[J liddy]

Originally Posted by Laird Scooby

From your description, it's either the sensor on the back axle or the wiring to it, just like Luke said further up.

You likely won't get any fault codes except perhaps on the ABS part, assuming your car is post 92 and has the Bosch ABS-2E system. If so, it'll say the "rear ABS sensor is faulty, open or short circuit or wiring defective" i believe is the exact words.

Before 1992, the Bosch ABS system was used which had no fault code capability.

The rear ABS sensor feeds not only the ABS ECU (sited above the injection ECU in the drivers kick panel area) but also the instrument cluster.

Dave if you read the bottom line of his 1st post the car is the car is a 1995 model so it will have the code reader set up