ABS Diagnostic Guide
Introduction
All Coupes came equipped with Bosch ABS systems as standard. The Coupe ABS is really very good, reliable and is not as intrusive as some systems on other cars.
There are two versions of the Bosch units. The 16v models have the older Bosch 2e system and the 20v models went on to a newer 5.3 model. The good news is that the newer 5.3 system has the same self diagnostic codes as the older 2e. The ABS ECU is installed on top of the ABS pump and is independent of the engine ECU.
MOT Issues
In order to pass the MOT the ABS light must illuminate and then extinguish. There is no point just removing the bulb. ABS must go through the correct sequence or it's a fail.
Diagnostic
Diagnostic Socket
There's an oblong fuse box by the bulkhead on the LHS (viewed from the driver's seat) with 40 and 60A fuses. The ABS diagnostic connector is clipped to the side. You should be able to make out A, B, C, (or 1,2,3 on some versions) stamped into the connector housing.
Running a Diagnostic Check
Earth Pin A of connector T8 .
Now turn on the ignition and count the ABS light flashes.
The first number will be 12 which is 1 flash, pause, 2 flashes then 12 another 2 times.
Fault Codes
Now comes your fault code. The system can spew out up to 3 codes.
16- Faulty LH Solenoid Valve
17- Faulty RH Solenoid Valve
18- Faulty Rear Solenoid Valve
19- Faulty Safety Relay
25- Incorrect number of phonic wheel teeth
35- Faulty Pump Motor
37- Faulty brake switch
39- Faulty LH sensor front
41- LH front sensor not connected
42- Faulty RH sensor front
43- RH front sensor not connected
44- Faulty LH Rear sensor
45- LH Rear sensor not connected
46- Faulty RH Rear sensor
47- RH Rear Sensor not connected.
48- Insufficient supply voltage
55- Faulty ECU (ABS)
56- Faulty power supply (Check 60A fuse)
When you start getting 3 12s again it has finished.
Dealing with Faults
First Actions and General Maintenance.
A whizz round the toothed speed ring with a wire brush is worth trying first as is ensuring the sensor is clean and not covered in iron filings.
Clean the sensor and check that no metallic grit is trapped between it and the toothed ring.
The power supply to the ABS unit is a thick wire from the battery via a corroded 60A fuse. Cleaning up the fuses by the LH strut, then turning the ignition on/off is the way to try and clear the fault. The system goes through a self-test when it powers on so while the voltage may seem OK it might not be OK when the pump is being activated and a lot of current is being drawn. Internal faults have also been cleared by cleaning up the 60A supply fuse contacts with active flux which you can get from the plumbing section in any DIY place for £2 a tub. The 60A fuse MUST be fitted correctly: it's easy to get that wrong and for it to be loose in it's socket.
If the above fails then move on to the sensors themselves.
Wheel Connector Faults
There is only one connector for each wheel. This connects the main ABS wiring loom to each sensor.
It is white, it has a black round section wire both sides.
Front Sensors
When you take the wheel off you'll see the abs sensor and the lead disappearing up into the engine compartment (impossible to reach) but the connections are up at the top of the engine compartment on the bulkhead
Check those connections: make and break them and squirt some WD40 in them. It could be the sensor is u/s but it's a fairly simple magnet/coil arrangement, more likely grit and grime stuck around it, clean and recheck the error after a drive.
The sensors themselves aren't unreliable but the lack of strain relief at the connector is. If you have a spare connector with wire, just chopped the connector and 10 cm of wire off at the sensor end, solder in the new one.
Rear Wheel Sensors
The rear ones live behind the rear three quarter panels and will require removal of the rear bolter seat cushion in order to access. There is a how to guide for this. If you are lucky they may be under the back seats. Clean the connectors or dispense with them and solder instead.
Testing the ABS Sensors
Apart from the obvious checks of ensuring there are no splits, cuts, tears, burns or chaffing in the cables from the sensors, and after confirming that the sensors are plugged into the connectors within the car, there are a couple of tests we can carry out to isolate faults.
We’ll start first by checking the resistance from the sensor.
You’ll need a Digital Multi-Meter (DMM).
Start by jacking the car up at the wheel to be tested. Make sure the car is securely jacked up, use wheel chocks to stop the car rolling and axle stands in case the jack fails.
Locate the sensor cable and the two-pin plug. As mentioned previously, for the front wheel sensors these plugs are located close to the suspension turrets. For the rear wheel sensors the plugs will be either under the rear bench seat or (more likely) behind the ¾ panel adjacent to the bench seat.
Disconnect the plug and identify the lead coming from the sensor.
Switch the DMM to read Ohms and connect to the lead coming from the sensor.
Spin the road wheel and you should see a variation in the resistance. If there is no variation then the cable, connector or sensor is faulty.
Now we can check the voltage.
To check the voltage you will need to use two flying leads. These are leads of thin wire which, when connected to the pins in the socket can be led back to the DMM.
Be sure that the flying leads do not touch each other when the connectors are pushed together.
Be sure also that the flying leads do not touch bare metal.
Set the DMM to read volts.
With the flying leads in place and the connectors plugged together, switch on the ignition. You should now see a voltage reading. Rotate the road wheel slowly and watch the voltage vary: it should change between +5v and +12v.
No change in voltage indicates a faulty sensor/wire/connection.
No voltage indicates a supply fault and you should check fuses and the main connection at the ABS module in the engine compartment.
Replacement sensors
You'll only get one from Bosch now, unless you can find a Fiat parts dealer with NOS (not Nitrous Oxide Systems!!). Details for ordering one from Bosch are in the FAQ section, the 'NS51' item number wasn't recognised, but they found the item description.
Replacing Sensors
They are a nightmare to replace and removing a front sensor will probably destroy it, unless you are very lucky. So buy new ones before you start removing the old.
The sensors are held on with an Allen bolts which will round and break under any sort of stress, such as a severe stare with your eyes
Then it's the fun job of getting the sensor out At least if you're replacing the sensor you don't have to be gentle. Just drill it out and replace. Best done by drilling around the outer edge of the sensor (you won't be able to drill right through the middle), then usually brute force to smash it to pieces, comes out quite easily after that.
Another old tip for removing the sensors, which I've recently been taught is to freeze them with CO2 spray.
Still Have problems
It is worth noting that after a session at the rolling road your ABS light may come on. Something about sensors getting very confused etc….A good hard brake will sort it though.
The ABS ECU may well have to be replaced. Failures are remarkably rare and it might be worth a visit to an abs specialist as there may be items they can fix/replace rather than resorting to the expense of a new unit.
Alternatively the ABS ECU can be removed from the pump without breaking into the brake hydraulics. There are a couple of companies on e-bay that will fix the ECU and send it back. You could also buy a fully recondition pump and ECU and only swap the ECU, leaving the brake pipes attached.
Contributors:-
Skinflint, Stan, Barnacle, Darlo Nick, Jammy Basturd, Sumplug and Rog20VT(Powerfiat) ep1, Theresa, Nobby
