Recommissioning a 480: 2. CEM & Relays

From CEM to VEM, from LED to lightbulb and more. If you have an electrical problem, like a broken info-centre, search for answers in this category. This is also the place to be when you expect the problem to be of an electrical nature...

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Posts: 27
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Location: Bradford, West Yorks

Recommissioning a 480: 2. CEM & Relays

Post by davekit » Tue May 17, 2022 4:42 pm

Part 1 is under ‘Secret Life’.

The Central Electric Module is well hidden in the passenger (LH) footwell, and there was a spare included with the car. This should have alerted me that there were faults! Sure enough, different ones on each, and some common faults which may have been independent of the CEM. Interestingly the car would still start without a CEM fitted.

One unit was very noisy, sounding like a box of crickets! With this unit fitted, the horn sounded randomly, the rear wiper did not work, the front wiper intermittent was not working (but otherwise ok), main beam, front fog, & spot (long range) lights not working, and headlamp washers came on with the lights down.

With the other CEM fitted the horn worked correctly, but the front wipers ran continuously and could only be stopped by removing the fuse! Other faults were much the same as with the noisy unit fitted, so were they down to the CEMs or something else? I did wonder how the car had passed its last MoT, only a month before I bought it.

I found a view of the inside of the mk.1 CEM on the forum with most of the relays therein identified, but the main relay box (under the bonnet) is missing the sheet identifying each relay – can anyone help for a 1987 car? The Haynes manual only shows a relay box for a 440/460 which is very different, and the Owner’s Manual only identifies the fuses (under the dashboard), which fortunately matches the sheet in the fuse box.

I can’t find the view of the CEM on the forum now, but fortunately I had printed it off. For completeness, these are the relays in the CEM, identified by the etched numbers on the pcb (rather than the superimposed numbers on the original post). I have added the rear wiper delay, which revealed itself while fixing that (see part 4).

REL 1 Windscreen wiper delay (front)
REL 2 Interior light
REL 3 Headlamp main beam
REL 4 Headlamp washers
REL 5 Indicators
REL 6 Wiper delay (rear)
REL 7 ?
REL 8 Heated rear screen
REL 9 Horn

The relays in the main box are identified by letters A-L. From the wide end:

--E------F ---- E missing; F tall, headlamp motors?
-----J-K ------ K missing
------L -------- Large cylinder, bulb failure (front)

There are also a few isolated relays in various locations. Can anyone fill in the blanks?

Back to the CEMs! I found someone willing to have a look at them. Nothing could be done with the quiet unit, but the noise on the other unit was down to a faulty voltage regulator. It was supplying 8v instead of 5v (not 12v which you might expect) and repeatedly firing all the relays, hence the noise. I think the voltage regulator is the transistor with the heatsink, opposite corner to the sounder (large round thing). With this CEM refitted, the horn now worked properly, the headlamp washers behaved, and the front wipers still parked. The rear screen heater also worked, but not the heated seats. Whether these were working or not beforehand, I can’t be sure. Most of the other faults remained, so it was unclear whether there were more problems in the CEM, or if they lay elsewhere. It proved to be the latter.

480 Newbie
Posts: 27
Joined: Sat May 14, 2022 11:16 am
Location: Bradford, West Yorks

Re: Recommissioning a 480: 2. CEM & Relays

Post by davekit » Mon Jun 20, 2022 10:30 am

My local friendly auto electrician has unfortunately retired, and is moving away from the area, but has shed some light on various issues. Yesterday he passed on a data sheet identifying the relays and sensors on 480s up to 1990. I will try to upload this when I have a chance. Meanwhile, by way of answering my question above, these are the relays in the box for 1986/87 models:

A-Headlamp----B-Fog lamps----C-Ignition----D-Auxiliary circuits
E-Air con I if fitted----F-Headlamp retractor
G-Fuel pump----H-Fuel injection I
J-Headlamp dim-dip I----K-not used
L-Bulb failure front

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