D1 interior lights flashing - AND solution

I came across an odd problem and found the solution, which I haven't seen documented elsewhere, so I thought I'd post it here in case someone in the future has the same issue.

1997 Discovery I. When I opened the driver's side front door (and that door only), the interior dome light, as well as the red light by the key, would blink twice, pause briefly, and then blink 5 more times. The truck seemed to run fine, except for a couple of little things: 1.) when you opened the door with the key in, there would be a constant tone, rather than the normal chime; 2.) The transfer case could not be taken out of High range; i.e., it was locked.

'couldn't find any mention of this in RAVE. It turned out to be a blown fuse, F12. This is one of the MFU fuses; the MFU does drive the dome light. 'must have blown it while I was troubleshooting the cruise control.

Icannap1 said:

Did you get your cruise control sorted out?

Click to expand...

Not yet but I've made progress. The vacuum lines were shot and I fixed those. Then I followed the test procedure detailed here: https://www.landyzone.co.uk/land-rover/disco-1-cruise-control-repair.231884/ NOTE: the Speed Sensor Test described there is incorrect. It appears the speed sensor puts out a square wave, and I measured an average voltage of about 8 volts no matter what speed I was travelling. My multimeter has a frequency (Hz) scale, and I confirmed that the frequency does increase as you drive faster, which is what I would expect.

Anyway, all those tests passed, so I assume the problem is with the cruise ECM. I took it out and opened the case, cleaned the relay contacts, and removed the pump driver transistor since I thought it was the most likely part to fail. It tested good, though, so it must be something else. 'looking to get a replacement; or I may send it to Module Master, or switch to the D2 ECM like some have. 'wish I still had access to an oscilloscope like I had when I was working.

Yes that's what I meant by "square wave". Speedometer works fine. It behaves per the manual: "This signal is a pulsating voltage, and its frequency changes with vehicle speed".

Ended up sending the ECM off to Module Master. Got it back quick with a 5 year warranty. And I now have working cruise! arty:

$65 flat rate plus shipping. On the invoice: "Faulty components replaced. Board reflowed and sealed. Cruise control has been tested. Cruise control has 5-Year Warranty".

I know for sure I got back the same unit I sent them. I could have bought units off eBay that were pulled from parts cars for about half the price, but there's no way of knowing if they work, and no warranty. I just wish I had gotten it before last weekend, when I did a 400+ mile road trip.

Their Search By Vehicle function on their website isn't very good; I looked it up by function. The Hella unit they fix is the one used in Disco I's, and a bunch of other makes/models: https://modulemaster.com/rebuilds/shop/powertrain/cruise-control/hella/

And as I mentioned previously, I figured it had to be the ECM, since everything else passed the Landyzone test procedure I referenced above (once I fixed the vacuum lines).