LX450 No Communication to ECM but engine runs

[AndoFZJ]

96 lx450
I'm unable to communicate with my ECM thru any scan tool I try. Even when using an old toyota tech tool. I rebuilt my motor and had the harness out and unplugged. The truck starts, runs great and shifts. I am getting the o/d off blinking while driving so I need to scan it for codes to look into the trans dtc. My odb2 port has power, grounds and continuity to the ecm on the communication wire. I've tried a battery reset. Has anyone run into this before? Any thoughts would be very appreciated. Thanks.

 

[60 toy ota]

I would verify continuity between the obd2 pins and the respective pins at the ecu connector

 

[AndoFZJ]

I would verify continuity between the obd2 pins and the respective pins at the ecu connector

I have found power and grounds at the obd2 port and it will power up scan tools. I also have found continuity on the communication wire at the obd2 port to the ecm.

 

[AndoFZJ]

I was welding on the vehicle but the battery was not connected. The ECM was plugged in. I know this is a debated concern. I have welded on this vehicle along with many others without any issues. The ECM motherboards look brand new with no burn marks or corrosion. I went thru the ECM power source testing and it has power from the fuse and main relay plus good ground. Given the vehicle starts and runs fine I didn't think I was going to be missing power and grounds but just going thru as much testing I can.

 

[jonheld]

I have found power and grounds at the obd2 port and it will power up scan tools. I also have found continuity on the communication wire at the obd2 port to the ecm.

The OBD2 port has 4 connections and the data connection is a shielded cable from the ECU E7 pin 6. The shield must be grounded and runs through connector IL2 pin 8 to ground point EC.

 

[AndoFZJ]

The OBD2 port has 4 connections and the data connection is a shielded cable from the ECU E7 pin 6. The shield must be grounded and runs through connector IL2 pin 8 to ground point EC.

View attachment 4114920

I saw that on the diagram. I have cleaned those ground points. I need to still get to that connector and insure it has continuity. Thanks!

 

[AndoFZJ]

The OBD2 port has 4 connections and the data connection is a shielded cable from the ECU E7 pin 6. The shield must be grounded and runs through connector IL2 pin 8 to ground point EC.

View attachment 4114920

I tested and I found continuity from IL2 to EC. I also found a few strands of the shielding sticking out of the blue wrap around the white communication wire at the obd2 connector and verified continuity down to the IL2 connector. Not sure what else to check... : ( I wish I had a spare ECM to plug in and see if I could talk to it in order to rule out the ECM.

 

[PIP]

I have a couple extra 95-97 ECM's. $100 shipped?

 

[AndoFZJ]

I have a couple extra 95-97 ECM's. $100 shipped?

Possibly, I'm going to do some more testing but will likely take you up on that. I can't see why it would fail and with no evidence of damage on the boards. At that price it would be worth a try. I assume they are compatible, plug and play and from running vehicles?

 

[PIP]

Possibly, I'm going to do some more testing but will likely take you up on that. I can't see why it would fail and with no evidence of damage on the boards. At that price it would be worth a try. I assume they are compatible, plug and play and from running vehicles?

Send me the numbers off yours and I should be able to match it. Yes, from running 80 series. If there was any issue I would make it right.

 

[jonheld]

Possibly, I'm going to do some more testing but will likely take you up on that.

You tested continuity between the data pin and the ECU, tested continuity between shield and ground.
I would test for a short between data and ground before replacing the ECU.

 

[PIP]

Something to consider- normal meters do a poor job of finding shorts.

The best tool for finding shorts is a Megger.

Meggers test continuity at very high voltage giving a clear picture of what's going on. Definitely make sure you remove your ecm before using a megger though.

I use meggers frequently. They Definitely find major issues where a regular ohmeter says things are fine.

 

[TheBussman]

I have seen one that ran perfect but had no communication and all good wiring, a used ECU fixed it. i currently have a bad ECU that has a failed fuel injector driver but good communication, free if you want to pay shipping and try it as a test. Or get one from PIP that works and you may fix your issue.

 

[60 toy ota]

Something to consider- normal meters do a poor job of finding shorts.

The best tool for finding shorts is a Megger.

Meggers test continuity at very high voltage giving a clear picture of what's going on. Definitely make sure you remove your ecm before using a megger though.

I use meggers frequently. They Definitely find major issues where a regular ohmeter says things are fine.

Do you have a recommendation for a megger that's budget friendly for a weekend mechanic/electrician? I don't need to validate 200' parallel runs at 480v/3ph like I see most used for

 

[PIP]

Do you have a recommendation for a megger that's budget friendly for a weekend mechanic/electrician? I don't need to validate 200' parallel runs at 480v/3ph like I see most used for

I have both a cheap Amazon one and a real Megger built Megger. The cheapy works fine.

I have a cnc machine shop and use a megger frequently to check wires. Mostly wires that move when an axis does. An ohmeter will say the wires are fine, then I hook the megger up and it's a totally different story.

 

[manofthewoods]

I have both a cheap Amazon one and a real Megger built Megger. The cheapy works fine.

I have a cnc machine shop and use a megger frequently to check wires. Mostly wires that move when an axis does. An ohmeter will say the wires are fine, then I hook the megger up and it's a totally different story.

Thanks the background.
I learned something completely new.

 

[60 toy ota]

I have both a cheap Amazon one and a real Megger built Megger. The cheapy works fine.

I have a cnc machine shop and use a megger frequently to check wires. Mostly wires that move when an axis does. An ohmeter will say the wires are fine, then I hook the megger up and it's a totally different story.

Good to know! I think it's time I convince the small business I work for that it's time to invest in one. Would've been helpful in diagnosing some wire chafing on our old cnc's as well

 

[AndoFZJ]

*UPDATE*

I did some of the ECM testing but couldn't find anything out of spec. I ended up buying the ECM off of PIP and can now connect with the scan tool! Just did a quick test start and she started right up. Hopefully the bad ECM was the cause of the "o/d off" light blinking close to the end of my last test drive. Time will tell. Thank you all for your help.

 

[alia176]

I was welding on the vehicle but the battery was not connected. The ECM was plugged in. I know this is a debated concern. I have welded on this vehicle along with many others without any issues. The ECM motherboards look brand new with no burn marks or corrosion. I went thru the ECM power source testing and it has power from the fuse and main relay plus good ground. Given the vehicle starts and runs fine I didn't think I was going to be missing power and grounds but just going thru as much testing I can.

I know i'm late to the party but I wanted to address the welding thing. I can assure you that welding on our rigs with the battery connected will cause no harm. Muffler shops do this all the time on modern cars all day, so I wouldn't worry too much about not disconnecting the batt during welding. Still, I'm very curious as to what happened to the ECU!!!

 

[alia176]

*UPDATE*

I did some of the ECM testing but couldn't find anything out of spec. I ended up buying the ECM off of PIP and can now connect with the scan tool! Just did a quick test start and she started right up. Hopefully the bad ECM was the cause of the "o/d off" light blinking close to the end of my last test drive. Time will tell. Thank you all for your help.

sweetness, thanks for following up on this.