405 SRDT

[Paul Baldwin]

Ok, I appear to have sorted an issue I have had with this lately, fingers crossed and I might as well document it here so someone using Google etc in future has a chance of saving some time with a Peugeot 405 Bosch ABS Fault Problem Diagnostic Trouble Codes etc. AFAIK it's relevant to some 306's too as it uses the Bosch 2e system.

My problem was an ABS light that was locked on, refused to flash at all in the end. It should turn on for a few seconds and then turn off, this indicates that it is doing its self diagnostics and if happy after doing its checks the light should go out and stay out unless it finds a fault. Everyone I talked to about old skool ABS said check the wheel sensors and ABS rings on the drive-shafts first for rust, damage, loose rings (ooer) etc. My only problem with that was that the car is in very good condition underneath so I was somewhat doubtful.

After a bit of searching I found some info about it being possible to flash some fault codes. There is a grey sensor in a black plastic box right by the ABS unit. Apparently you can get a machine to translate the codes OR earth the pin with the visible terminal in it and it will flash the ABS light on the dash, count the flashes, refer to the list of codes et voila...

Diagnostic plug



Pump position



I grabbed the first visible switch I had to hand, earthed one end and stuffed the other into the diagnostic terminal.



The sum of that was jack shit, no matter what sequence I tried of earthing the output, ignition off/on/off for a few seconds/on etc with the switch in open or closed position the light stubbornly stayed on. Bugger!

I have previous with old pugs and their fun* electrical gremlins so next I set about finding all the main earth points in the engine bay, removed each one, cleaned the bolts and connectors up and re-tightened. I also cleaned up all the ABS pump connectors with switch cleaner and a small wire brush (with battery disconnected).



The sum of that was the sum of sweet FA difference.

I then moved onto the ECU itself. It's located under the scuttle panel and access is really very good even if the looms are a bit fiddly to get back in the right position afterwards. I removed it, sprayed it with switch cleaner but tbh all the contacts looked very good and I was doubtful it'd help. However the ECU did appear to have had water/condensation issues? I really cant fathom out why it showed such signs of corrosion. The panel protecting it was in place, no drains were blocked and I simply can't see how water could get to it!





I cleaned up the 3 other relays and another main earth hiding behind the ECU and put it all back together. Still no difference whatsoever. . I was up at a mates while doing these bits and pieces so made use of his lorry pit for 5 mins and had a look at the sensors etc from underneath, as I remembered all looked tip top.

Soooo, sum of it was I took a punt and ordered an ECU off Ebay for 20 quid delivered. It took me 10 mins to fit and I didn't even get dirty and it f*cking works!
That's my Xmas present to myself sorted anyway