Recently purchased an 01 disco II with 125,000 + on it. There have been many issues that I have managed to work out so far, the last one that has me stumped started with the diagnostic port just not working at all. I traced that to no power on the P wire to port 16. Corrected that by using a tap fuse on fuse 20 to power it. Powered up the scanner (actron & autologic). They connect but show no codes. The autologic is able to read other basic info so I have to think it is all working, but I still have a SES light I can not clear nor get codes for. I have no idea where to look next. Any thoughts or suggestions? (both scanners have been tested on 2 other cars and work as should).

 

Tranny ECU can make codes, and only some of them make M&S lights flash. There are 7 computers on the D2 that can speak on the OBDII line. One may have a problem, has told ECU to turn on the SES (MIL) light, but can't tell the scanner about it due to some problem with that common header wiring. See attached from RAVE. Maybe you have to fault something on each of the computer supervised systems to see if you get a code...

 

Thats an important tidbit I should share. While doing my repair I had the battery pulled for awhile so the light of course was out. So I plugged in the autologic and took it for a drive waiting for it to come back so I could grab the code. At a red light (and i may have this wrong in my memory) I had put it in park for some reason, back into drive to go and got the blinking T and S. That tossed a code for something regarding the tranny getting a mis signal on the gear. Put in park, turned off, back on and the issue cleared but the light remains. Prior to this have had no other indications of an issue. I'm certain I need new plugs and wires, have cleaned the MAF and air box out. I know this truck is a problem child, but I like to think it deserves another chance Any thoughts on creating faults on the different systems?

 

Well, they may not generate codes, it maybe just the programming input for them, in some cases. But the ABS system has codes, etc., that you can't clear without the correct scanner. So unplugging something there might be a problem as well. So the Autologic shows MIL status as "ON" as well?

 

Neither scanner shows the light as being on or any stored codes. I even tried having the autologic run the clear all commands and the light remains. I do get the 3 amigo's on occasion which will be my next hurdle. I'm trying very hard to get this ready for inspection by the end of the month. I expected a faulty sensor or something somewhere, but without a code its driving me nuts quickly. For awhile it was not on all the time, then a couple times a flicker. Now it does not go out. Does that purple wire to pin 16 pass from any of the systems? My understanding was it was battery, Fuseable link 3 in the engine bay, fuse 20 in the the cab and then to pin 20.

 

Fuse 20 runs lots of other things via a couple of headers. If you go in the circuits drawings and search for FUSE 20 it shows up 11 times.

 

Yeah..been reading it lots. Makes my head hurt. I used an addon or tap fuse. So everything else on the fuse should remain untouched, i think. Put the tap in, used a 15 amp fuse to act as the original and a 10 amp wired direct to pin 16 on the diagnostic port.

 

If i'm understanding this correctly, you have a check engine light that the code reader/scanner can not locate. You also stated that on the OBD port, there was no power so you added power to the wire and now the scanner will power up, but still no code. If this is correct - by you adding power to that wire, you gave the scanner power to come on, but normally the ECM should be providing power to the wire. So it can't find a code because I don't think the ECM has full power. With the engine running - does the scanner show the proper RPM's / Engine Temp? I would think that you will need the wiring diagram and tract it from the battery to the ECM. Since it was randomly coming on and off for a while, I'm betting that when you tract the wires - you will find on that was rubbing and is now shorted or broken. Be patient - These are the issues that shops charge $500 to track down and cost $1 to fix.

 

Schematic posted above from RAVE shows OBDII port power from a battery fuse, not switched by ECU. If that is wrong diagram, please advise. IMHO if ECU had no power, it might be hard to get the vehicle to run. But please check F1 and F12 in underhood box.

 

Have checked and rechecked all the fuses and fuseable links. Maddening! Parked it last night, remote fob was working, this morning not working. Pulled the battery and did some cleaning in the engine bay. De greasing and connector cleaning. Plugged back in. Figured I'd clear the light and see if i get lucky. Drove 25 miles and thought I had gotten lucky! 28.5 miles..light back on. Stopped, scanned, no code. As for your diagram, same one I have and from what I see in the truck is accurate. I also have no dome lights, or light ring around ignition or cigar lighter. They were last on my list..but now im thinking things may be related. Next guess is to pull apart the wire bundle in the passenger foot well and see if I can find any issue around connecter 0289. After that...I'm real low on ideas.

Will be doing part of a tune up tomorrow, perhaps will help with clearing the code anyway but still need to get this sorted.