wwwent

Hi,

I just recently purchased a used 2004 MDX with 216,00 km. for a pretty good price. The engine sounded very smooth and quite. My wife and I loved the car.

Everything was fine until last week, I noticed there is a puddle of transmission oil on the driveway. So I parked over a clean spot. Next day, another oil spot appeared. I craw under to have a better look, found the driver side drive axle to the transmission is leaking. Upon further research on the net, I concluded that the problem is the oil seal. After a new oil seal has been installed, I accidentally over stretch the ABS speed sensor (Couldn't pull it out, fear I would break the plastic by force). When everything is done. I get VTM-4, ABS, VSD and ! with triangle light on. I suspect it must be the ABS
speed sensor fault. No DTC reported from OBD2 scanner. Just to be sure, I wanted to get the VTM-4 code by shorting pin 4 and pin 9 at OBD2 port.

Problem begin!!!
It has been a long day, and the port is placed upside down. I jumpered pin 5 and pin 16. There was a slight spark. And I couldn't read anything. I noticed I shorted the wrong wire, so I jumped 4 and 9. Got the code 21 which indicates front left ABS speed sensor fault. Then I plug in my OBD2 scanner. There was no OBD2 port detected. I try starting the car, the starter cranked, but no started. Also the shifter would not shift out of PARK. There was no power in Pin #16 (+12V). I checked every fuses (all four locations) including 7.5 A #9 Backup (ECU) Fuse. There is also no engine trouble light. According to ECU troubleshooting guide listed below, problem could be bad main relay or bad fuse. I also pulled the battery power for 1/2 hour, did't help. I hope I didn't fry the ECU.

Please help locate main relay, provide ECU wiring diagram or suggest other solutions. I might end up towing it to the dealer. I just don't want pay $$$$$ for someone to troubleshoot electrical (finding needle in haystack).

I want thank everybody in advance and appreciates all helps.

ECU Troubleshoot:
http://techauto.awardspace.com/ecu.html

OBD2 pin out

pin 4 (BLK) = chassis ground
pin 5 (BRN/YEL) = LG3 logic ground from ECU pin E3
pin 7 (LT BLU) = "K-Line" (2-way OBDII serial communications line) to ECU pin E23
pin 9 (BRN) = SCS (Service Check Signal) line to ECU pin E29
pin 12 (RED/WHT) = write-enable signal to ECU pin E30 (for rewriting the ECU)
pin 14 (GRAY) = +5V from immobilizer control unit pin 3 (probably for rewriting immobilizer codes)
pin 16 (WHT/RED) = +12V battery voltage (from #9 BACKUP fuse 7.5A)

OneBadTurboCRV

Very, VERY high possibility you fried the ECU by putting +12v directly to ECU ground. I would pull apart the ECU and see if you can spot anything or at least give it a good smell as an extremely basic test. If you are going to be fixing your own car then you really should buy a FSM.

wwwent

Thanks Badturbo, I stopped by the dealer this morning, John the mechanic seems to know what my situation is. He offered to print me a circuit diagram of the ECU so I may trace the circuit before towing it to them. Very nice gesture. I would post the diagram once I get it from him tomorrow. Couldn't find any ECU circuit on the net. Worst case, new ECU is $1000 plus repair cost. Not too bad. I was thinking $3k.

I understand FSM is a valuable tool for DIY mechanic. I have it for my TDI Diesel and Grand Cherokee Overland (jeep went for a swim last month, hence I pick up the MDX). MDX is not a true off roader, but on road is pretty sweet. My 10yrs old MDX beats all other 2-3 yrs old vehicles we look at. Better refinement and engine is smooth and quite. Newer cars are build much cheaper compare to old.

wwwent

More help needed.

Where can I locate the ecu unit. Behind the Radio console, I found the Bose Sound module, Airbag Module, Yaw Rate Sensor, and Temperature Climate control module. Nothing behind the glove box, and nothing by steering column.

wwwent

Found it. ECU is located under the hood, not inside the cabin.
In case anybody wants to know it's behind coolant reservoir.