Corolla OBD Failure

You have a data port along the bottom edge of the dash board in the area where your left knee goes while you are driving. Some Auto Parts stores will let you use the OBD II Code Reader for free in the parking lot of the store, and some will let you take the reader home - they will show it as a sale on your credit card, then give a full credit when you return the tool.

I would be using the code reader to take a look at the computer system in the car. If the computer really is toast, you'll need to buy a new one.

Where in IL is the OP? I'm willing to do a scan with my OBD II scan tool if the OP is reasonably close to me.

I'm in the Chicago metro area.... I'd really appreciate any/all help to get this resolved.

Thanks, Nirav

Ray, I haven't ever heard of a computer shutting down like I think he is saying. I suppose it could happen, but wouldn't there be a blown fuse or something along those lines to be looking at first? I am a bit mystified how the Check light can be working and the computer not be working.

I would highly doubt that the ECU would be the culprit... my guess is there is a bad/loose wire to the OBD connector... I may dig around for a OBD-II pinout to see if I can check for basic voltages etc.

Thanks for the help so far!

Nirav

Nirav,

ECU's have an extremely low failure rate - so low that the company that checks ECU's returned for warranty repairs for Toyota sees only 1 or 2 bad defective ECU's every 5 years or so. The rest of the ones they check have either been damaged or check good.

The OBD connector is under the driver's side of the dashboard. It will be shaped somewhat like a PC's parallel connector, only fatter.

Where in the Chicago area? Northwest suburbs?

No problem. I have this nagging suspicion that the guy at the inspection station has been smoking his medical marajuana at lunch. I'm stuck on the feeling that if the computer was completely out, then the car would be running at all. I suppose it could be hard wired to a Safe Mode, but it seems to me that if it was operating in the safe mode, the check light ought to be on.

I'm right at I-355 and I-88... so I can go anywhere (if traffic is on my side) within 1/2 hour to 45 mins. I had the same problem during emission testing 2 years ago - but at that time they let me do the actual dyno tests because the new testing laws were not in effect yet. I had to get retested (2 yrs have passed) so I went over lunch, and they failed me because their computer wouldn't communicate with the OBD port (you mention). When it happened 2 years ago I just brushed it aside as an one-off failure with their system - but now that it happened again, I'm fairly certain there is something wrong with the vehicle.

I am familiar with the OBD-II connector - in my other vehicle (a Nissan), I am able to follow a sequence of silly steps to have the the OBD system blink out the codes. No such feature on my 97 Corolla.

I would think that a bad ECU would cause other issues with the car and (knock on wood) there have been none.

Nirav

Jeff,

I wish I could blame the tester, but since this has happened two test cycles in a row (on different equipment, 2 years apart), I'm sure there is a problem at my end. The car drives fine - no issues whatsoever, so I'm really hoping its just a bad wire. Any pointers to a pinout for the connector where I can possibly verify some voltages/grounds to help trace a bad wire?

Nirav

Jeff Strickland wrote:

A Bad ECU would probably cause other issues with the car so you can probably rule that out.

Visit a local auto parts store like Pep Boys or Auto Zone to see if they will do a free scan for you. If you do a scan and nothing comes up, then, if you have a multimeter:

Look at the check connecter (known as a DLC3 connector). There will be 2 rows of terminals/pins.

The bottom row (wide part of the DLC3) has terminals 1 through 8, counting from the lower right to the lower left. The top row (narrow part of the DLC3) has terminals 9 through 16, counter from upper right to upper left.

Terminal #7 is the pulse generator during signal transmission - voltage will be on-off.

Terminal #4 and #5 should always have less than 1 ohm of resistance between the terminal and body ground. Terminal #16 should always have between 9 and 14 volts between the terminal and body ground.

There are standard values for the ECU as well although I do not have that info handy. You can go to Toyota's web site and purchase info or try AllData for info.

I live in the Schaumburg area. If you want to travel that far, send me an e-mail.

Good luck!

Ray - that is great information. My initial plan of attack was to go to Autozone and see if they had the same troubles. If they did, I was going to try to jiggle the harness/connector and see if I could get it to work.

If that fails, I'll pull out the multimeter at home and go through the checks you posted. I will post back later this evening with my findings.

For Terminal #7, should I check for voltages pulses between #7 and body ground or do I need to check relative to one of the other terminals?

I do appreciate your offer of additional help, and all the responses so far!

Nirav

While you're at it, if you have any aftermarket accessories like a security system, remote starter, or stereo, make sure that nobody tapped into a wire leading to the DLC3 connector.

You're welcome!

Jeff, wouldn't you know it if the computer were toast?...I wouldn't think it'd run at all would it?...

That's what I was thinkin'.

I can't imagine how the OP could drive the car to the inspection station if the inspector was going to tell him that the computer doesn't work.

Terminal 7 is body ground. It would be good to confirm that it really is ground.

Good news!

I popped over to Autozone on the way home and their OBD-II scanner wouldn't pick up anything either - just dead. They let me play with the scanner for a bit, so I jiggled some wires but no luck...

Once I got home, I tried to measure the voltage and resistance across the various terminals that Ray had specified and NOT even one pin was "live" - no voltage, infinite resistance... I was glad in a way that every pin was reading open - since I was confident that a connector was not in place somewhere along the harness.

I took off the cover under the steering column and lo and behold, right in front of me was a disonnected harness. The DLC3 connector is on an

8" (or thereabouts) short harness. The other end connects to the main harness. That connector was completely undone. I imagine the connector was left undone when some work had been done on the car - since you have to undo the connector to remove the plastic cover from the car.

I plugged it in, checked the pins, and the readings "almost" as Ray had specified. For me Pin #7 voltage did not go on/off, other pins checked out as described.

I popped back to autozone, had the guys recheck and their scanner worked fine and reported "No Codes Found".

So now I'm off to the emissions place tomorrow again. Hopefully they won't pull their "This repair has to be certified by an authorized shop card" on me.

Thank you all for your help!

Nirav

97 Corolla DX, 72k

It sounds like your problem is solved! The pulsing voltage from Pin #7 is only when it is relaying info.

Good info. once again. I appreciate your help.

Nirav