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Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.


Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.
Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.

Car: 1999 Rover 800 820 Auto Fastback

Colour: Charcoal Grey / Black

This particular Rover 800 has always had an unusually large appetite for chomping through front ABS Wheel Sensors, and therefore would often have the ABS warning light lit up on the dashboard! Usually we would run the Rover800 ABS Self Diagnosis and replace the faulty ABS sensors in time for the annual MOT test in order to extinguish the warning light, even though it was not a requirement.

Although we did not actually have to have the ABS working for the previous MOTs, a change in the law in 2012 and with the warning light back on once again, we had no option but to sort it this time.

With a spare sensor in stock (passenger side one), we replaced the faulty front drivers side sensor (not easy, but do-able!).

This time though, when we extinguished the warning light, a new fault emerged, instead of the ABS warning light coming on for 2 seconds when the ignition was switched on, we had the problem that the warning light was not coming on at all!

We knew it was not the replacement ABS lead that we had fitted, because we were able to confirm that that worked by testing it connected up on the coupe.

The problem then became an intermittent one, and sometimes the warning light would work, but sometimes it would not! While the light was in working mode we were able to check and no fault codes were showing up!



Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.
With the ABS Warning Light bulb playing up on the dashboard, we decided to start by checking the fuse (easiest thing to replace!) then the bulb, just to eliminate them both from our enquiries!

Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.
After swapping a few dashboard bulbs around all seemed to be working fine and so we would have to look elsewhere for a solution!

Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.
The ABS ECU is located under the bonnet.

Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.
Next we disconnected the main hank from the ABS unit under the bonnet & the warning light would come on constantly & putting the hank back would extinguish it (the battery was connected at this stage). This confirmed the warning light bulb was in fact ok!
Had we done this check first we would not of had to dismantle the dashboard!

Looking at the Rover 800 wiring diagrams, the warning light bulb is fed from Fuse 16 and earths via a red/blue wire through the ABS Electronic Control Unit. So as the fuse was ok, this meant we should be looking at the ABS ECU.

From the wiring diagrams we were able to establish that connecting a pin to the red/blue wire in the hank and then wiring this directly to the earth on the battery the warning light will should come on.

So here is what you need to know to locate your own fault;

IF YOUR ABS WARNING LIGHT DOES NOT LIGHT UP WHEN THE IGNITION IS SWITCHED ON

1. Disconnect the Hank of wires at the ABS unit under the bonnet. The ABS Warning Light should now light up permanently. If it does not, try changing Fuse 16. If this fails, then replace the ABS Warning Light Bulb in the dashboard.

2. If the light does light up permanently when the hank is disconnected, re-connect the hank and use the RED/BLUE wire in the hank to help provide the answer!
Put a pin in the red/blue wire, connect 1 wire from a multimeter to it and the other multimeter wire to the battery -ve/earth.

The results should be as follows:

WHEN THE ABS WARNING LIGHT IS WORKING CORRECTLY;
Ignition OFF: No Warning Light. & 0 Volts
Ignition on (Position II) for first two seconds: Warning Light. & 1.6 Volts
Ignition on (Position II) after first 2 seconds: No Warning Light. & 12 Volts

------------------------

when NO ABS Warning light is showing;
Ignition OFF: No Warning Light. & 0 Volts
Ignition on (Position II) for first two seconds: No Warning Light. & 0 Volts
Ignition on (Position II) after first 2 seconds: No Warning Light. & 12 Volts

-------------------------

on a car with the ABS Warning light permanently on;
Ignition OFF: No Warning Light. & 0 Volts
Ignition on (Position II) for first two seconds: Warning Light ON. & 1.6 Volts
Ignition on (Position II) after first 2 seconds: Warning Light ON. & 1.6 Volts

------------------------

Our results correctly matched the middle set of results above, (and correctly matched the top set when the light was intermittently working for us!).

With correct results we knew that the fault was within the ABS unit, and was most probably just a broken solder joint/bad connection. (which after looking at a few car ABS ECU repair videos on youtube, seemed like it would be easy enough to fix!)

Had the multimeter showed 0v for all three readings, then the fault would be in the wiring loom, dash panel, fuse, etc! (and probably take forever to find!)

So now we knew the fault was within the unit, it was time to strip/repair the ABS ECU.

Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.
To make things easier we had to swing the Engine Bay Fuse Box out of the way!

Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.
With the fuse box undone, it was then possible to access the 4 Torx head bolts to remove them.

Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.
Hmmm! With the Torx head bolts removed, the ABS ECU did not seem to want to come apart!

Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.
Trying to prise it open here did not seem to be working either and we did not want to bust it open as we did not know if we were going to break anything!

Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.
Resorting to the forums and with a little help from a Rover owner in Croatia, it seemed there was something else to undo further down on the unit, just as we had begun suspecting!

Hidden underneath the domed bolt and rubber bung, is another bolt which is still fastening the whole unit together!

Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.
Here you can see the hidden bolt!

Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.
No wonder we could not just split the unit open! Just look at the dam size of that bolt!

Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.
With the ABS ECU unit now opened up, it was clear to see that it would be far too difficult to work on, as the circuit boards and plastic moulding were all machine pressed into the metal casing!
...also a clear silicone gel covers the circuit boards :(

Rover 800 820 825 827 ABS Warning Light Bulb & ABS ECU.
Luckily we were quickly able to replace the half we needed with another one from the scrappers.

Taking the tools with us, we split open an ABS unit in the scrappers (It happened to be on an 800, but we could have got one off a 200/400).
By opening it up we just purchased the half we needed rather than buying the whole unit and motor, meaning we got it at a better price ;)

The replacement unit works great! & Hopefully it won't chomp through ABS Sensors at the rate the previous one required!




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