OBD non-connection error

[LardOfTheDance]

2003 p5

Just failed NJ inspection because they couldn't establish a connection to my on board diagnostic. I understand it may be impossible to disgnose this without spending some time with the car. A search here at 247 didnt yield any results. I can tell you the cig lighter works fine. The only after market mod i am aware of is a break light hook-up for pulling small trailers or whatever.

So coupla questions:
1) likely problem? Likely solution and $$$?
2) worst-case scenario? $$$?

Thanks in advance for any guidance you may be able to offer.

 

[DarkAngel]

Anyone around you that can lend you an ECU? Weird that it doesn't want to connect. Did you also check the OBD connection under the dash for any wires that may have been cut or modified?

 

[LardOfTheDance]

Dark angel, thanks for taking an interest in this case. I just looked under the dash at the obd port. Nothing looked cut or damaged or modified.

Any other guesses? I gotta tell you the car is BULLET PROOF. I've had zero problems with it. It runs like a dream. Im on a road trip as we speak. I'm baffled.

 

[Tekk]

probably shouldnt be posting and driving ;]

but i had that issue as i was trying to get mine tuned. i dont have i guess that thourough of an inspection here, nor do i have emissions, i ended up needed to replace my ecu.

 

[LardOfTheDance]

Do not read this if u r driving. It can wait.

Thanks tho tekk. Let me ask how much the new ecu set u back?

 

[Tekk]

i took it out of my parts car, so free? just go to a scrap yard IF you can.

only reason i said what i did was cause of Im on a road trip as we speak

 

[CheeseHelmet]

Do not read this if u r driving. It can wait.

Thanks tho tekk. Let me ask how much the new ecu set u back?

Depends where you get it, my local self-serve scrap car lot only charges $15 for an ECU. If you can't find any obvious damage perhaps you can try to scan the car with another OBDII tool (autozone will scan your car for free), it could be that the shop you went to had a faulty scanner.

If that doesn't work, grab a copy of the wiring diagram (available here) and a multimeter. On page "B-2e" you'll find the schematic for the link between the OBD port and the ECU connector, unplug the ECU and test for continuity on the two data lines, the ground lines, and then check that you get battery voltage on the appropriate pin of the OBD connector (blue/red wire).

 

[LardOfTheDance]

Hahahahah me=dope. Thanks. Fyi im at my parents kitchen table in VA. Not driving and posting. Breathe easy.

Im not by any means even a novice wrencher so pardon the following question: will the car run if the ecu is faulty? The ignorant and uninformed (me) would think that the ecu is critical to the operation of the vehicle. If that were true... Shouldnt it be running really funny or maybe even not at all?

 

[LardOfTheDance]

Thanks cheesehelmet!! This is why im quickly falling in love with this site.

Im going to spend some time on this maybe tomorrow or sunday. One small thing: where is the ecu itself located?

Depends where you get it, my local self-serve scrap car lot only charges $15 for an ECU. If you can't find any obvious damage perhaps you can try to scan the car with another OBDII tool (autozone will scan your car for free), it could be that the shop you went to had a faulty scanner.

If that doesn't work, grab a copy of the wiring diagram (available here) and a multimeter. On page "B-2e" you'll find the schematic for the link between the OBD port and the ECU connector, unplug the ECU and test for continuity on the two data lines, the ground lines, and then check that you get battery voltage on the appropriate pin of the OBD connector (blue/red wire).

 

[CheeseHelmet]

It's very possible that a part of the ECU is damaged (Eg. the OBDII bus transceiver) but that should not stop the whole ECU from working.

 

[CheeseHelmet]

Thanks cheesehelmet!! This is why im quickly falling in love with this site.

Im going to spend some time on this maybe tomorrow or sunday. One small thing: where is the ecu itself located?

It's in the passenger footwell, it's bolted to the opposite side of the metal plate hidden under the carpet. It's not that hard to remove, it's just a bit of tight spot to work in if you're not a tiny dude

 

[LardOfTheDance]

UPDATE: I took the car to AutoZone to see if possible it was a fluke with the OBD reader at the inspection station. AZ couldn't read it either. So this weekend for sure I have a date with a multi-meter. =(

I don't need to get it resolved technically until end of June, but I'm eager to see what the problem is.

 

[LardOfTheDance]

Do I need to remove these bolts (yellow arrow) to do what I gotta do? Or am I missing an easier way to do this?

It's in the passenger footwell, it's bolted to the opposite side of the metal plate hidden under the carpet. It's not that hard to remove, it's just a bit of tight spot to work in if you're not a tiny dude

 

[CheeseHelmet]

Do I need to remove these bolts (yellow arrow) to do what I gotta do? Or am I missing an easier way to do this?

Yep, there's 4 nuts, the two pointed at by the yellow arrows and an additional two further down on the floor.

You need to pull back the carpet some more, it'll make the job easier.

 

[DarkAngel]

I can't see your picture but I posted this one a while ago but it seems you have it figured out though.

 

[i12drivemyMP5]

There are a coupla 5 spd ecu's in the FS section here and a 48.00 shipped on ebay in you need one...........

 

[LardOfTheDance]

Questions about PCM to DLC links

thx for that reference DarkAngel. I still don't really know my away around the shop manual. I know it is all there but it is just a massive amount of information, especially for someone with only a little experience.

Speaking of inexperienced I want to ask you guys a coupla questions about the B-2e wiring diagram below:

First a few questions about the symbols (I can't find the legend)

1. What are the boxes X-01, X-05, etc.?? I'm assuming connectors
2. What is "JB-02" and "JB-05" in the circuit from the battery to pin1?
3. What is "FB-09" and "FB-05" in the same circuit?
4. What is represented by the circled letters?

Now about the actual diagnosis:

1. The circuit between the positive terminal and the first pin of the DLC (blue/red wire) is the only circuit with any fuses as far as I can tell. Is that the likely problem? I test this by touching one end of the meter to positive terminal of battery and the other to the first pin w/ blue/red wire, correct?
2. Should I disconnect the ground cable from battery when performing the test?
3. Then just test each pin of the DLC to all corresponding connections on the PCM, correct? (DLC pin 4 to PCM pin 13; DLC pin 12 to PCM pins 51,76,24,103,77; etc. etc.)

Thanks again in advance.

 

[CheeseHelmet]

First a few questions about the symbols (I can't find the legend)

1. What are the boxes X-01, X-05, etc.?? I'm assuming connectors
2. What is "JB-02" and "JB-05" in the circuit from the battery to pin1?
3. What is "FB-09" and "FB-05" in the same circuit?
4. What is represented by the circled letters?

The third and forth page of the wiring diagram PDF have a list of all the abbreviations used in the schematics.

• X: Common Connectors
• JB: Joint Box (the fuse box inside the cabin)
• FB: Fuse Block (the fuse box inside the engine bay)

The circled letters are the pin numbers for the huge ECU connector. See page B-2a for its pinout.

Now about the actual diagnosis:

1. The circuit between the positive terminal and the first pin of the DLC (blue/red wire) is the only circuit with any fuses as far as I can tell. Is that the likely problem? I test this by touching one end of the meter to positive terminal of battery and the other to the first pin w/ blue/red wire, correct?
2. Should I disconnect the ground cable from battery when performing the test?
3. Then just test each pin of the DLC to all corresponding connections on the PCM, correct? (DLC pin 4 to PCM pin 13; DLC pin 12 to PCM pins 51,76,24,103,77; etc. etc.)

Thanks again in advance.

1. I doubt a popped fuse is the problem, if the "ROOM" fuse were popped your radio wouldn't be working. Your testing method is correct, but you don't need to test all the way back from the battery (I'd pull the ROOM fuse and test from there to the DLC), but why not
2. Yes, always disconnect the battery and wait a few seconds before doing continuity tests, having the battery there could lead to a false positive.
3. Yup. For pins 11 and 12 you just need to make sure they're connected to pin 77 on the ECU connector (which should be connected to ground).

 

[LardOfTheDance]

Wow thanks again for quick reply. You've made this problem seem very manageable. I'll keep you posted.

 

[LardOfTheDance]

Diagnosis Results (1st Round)

Ok here's what we got:

• DLC PIN #01 > ROOM fuse: GOOD
• DLC PIN #04 > PCM PIN #13: GOOD
• DLC PIN #10 > PCM PIN #79: GOOD
• DLC PIN #12 > PCM PIN #77: GOOD
• DLC PIN #13 > PCM PIN #77: GOOD

New ECU is in order I'm assuming??