ODB2 not communicating?

Tiny
BFERKINS
  • MEMBER
  • 2002 TOYOTA AVALON
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 140,000 MILES
My scanner tool powers up but when I turn on the key it fails to communicate and gets an error.

I checked the following:
1. ODB fuse is good.
2. I get power on pin 16 of ODB port.
3. I made the female pins smaller on the ODB port to confirm the pins weren't too loose to make a connection.
4. I had an extra ECU that I put in for a quick test and still see the same issue.
5. Voltage I measure on the pins when I turn the key on. Gnd to pin 7 - 8.3V, gnd to pin 13 - 11.04V, gnd to pin 14 - 11.35V.
6. Started to unplug sensors one at a time but can't find them all.
Wednesday, July 16th, 2025 AT 9:46 AM

17 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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Have you tried the scanner on another car? Sometimes the scanner themselves are bad. I would also check the EFI 1 fuse 7.5 amp and the EFI relay to make sure they are working which is under the hood fuse panel. Here are the ODB2 wiring diagrams so you can see how the system works. Please go over this video as well.

https://www.youtube.com/watch?v=6Tlg3JmgNSQ

Check out the images (below). Please let us know what happens.
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Wednesday, July 16th, 2025 AT 7:29 PM
Tiny
BFERKINS
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Hi Ken.

This all started when I brought my car in to get it smogged, and they ran into a computer problem. I did, however, double-check that my scanner works on my other vehicle. I also confirmed the EFI 1 fuse is good, but for the relay, should I just confirm the resistance across the coil is between 50 and 120 ohms?

I watched the video, but it doesn't apply given that the port has power and the tested powers up.

Thanks!
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Wednesday, July 16th, 2025 AT 9:41 PM
Tiny
KEN L
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Yep, you can test the relay but this won't always work because the coil is not under load when testing, but if it is shorted or open that will show up. Let me know how it tests.
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Thursday, July 17th, 2025 AT 10:09 AM
Tiny
BFERKINS
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I tested the relay, and it's in spec resistance-wise (109 ohms), and I confirmed it was working by pulling it out and trying to start the car, which it did not.

What should I try next?
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Thursday, July 17th, 2025 AT 10:22 AM
Tiny
KEN L
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Do you have 12 volts and pin # 13 lt grn/red with the key on?
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Thursday, July 17th, 2025 AT 12:47 PM
Tiny
BFERKINS
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I have 11.04V on Pin 13 when the key is on.

Pin 7 - 8.3V, pin 13 - 11.04V, pin 14 - 11.35V.
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Thursday, July 17th, 2025 AT 1:22 PM
Tiny
KEN L
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So at the battery you have 11 volts?
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Thursday, July 17th, 2025 AT 5:13 PM
Tiny
BFERKINS
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At the battery, I have 12.35 volts, which I also have at pin 16.
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Thursday, July 17th, 2025 AT 8:24 PM
Tiny
KEN L
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Does the wht/blk wire have a good ground? Pin 4?
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Friday, July 18th, 2025 AT 9:13 AM
Tiny
BFERKINS
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Yes. I checked the continuity between pin 4 and 5 and to chassis ground and it's good.
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Friday, July 18th, 2025 AT 9:29 AM
Tiny
KEN L
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Lets check the white wire from the connector to the PCM. Let me know
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Saturday, July 19th, 2025 AT 9:25 AM
Tiny
BFERKINS
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Pin 7? That is reading 8.3V
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Saturday, July 19th, 2025 AT 5:54 PM
Tiny
KEN L
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Yes pin 7, you must unplug the PCM and check the continuity between the connector and the PCM.
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Sunday, July 20th, 2025 AT 10:10 AM
Tiny
BFERKINS
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Confirmed that I have continuity between pin7 of the ODB connector and the ECU connector with the same white wire.
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Sunday, July 20th, 2025 AT 4:34 PM
Tiny
KEN L
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Hmm, I know the engine runs but the diagnostic program inside the PCM must be bad. You tested all of the wires for continuity, power and ground, so the PCM is the only thing left.
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Monday, July 21st, 2025 AT 10:10 AM
Tiny
BFERKINS
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As stated above in the first post, I already tried another ECU. I just reconfirmed that the other ECU didn't fix the problem. It's a used (tested) ECU I bought off eBay from a reputable resaler that says it's tested. The ECU is not programmed for this vehicle (chip in key), but it powers up, and I can turn over the engine. The ODB won't communicate with it when installed like the original one. I also reconfirmed the ODB tester works on my Jeep to ensure I didn't short anything out in the last wave of testing.

Any other ideas?
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Monday, July 21st, 2025 AT 11:31 AM
Tiny
KEN L
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I am sorry I dont have anything else to try.
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Monday, July 21st, 2025 AT 5:41 PM

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