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Has anyone come across the above fault on an ISF? I tried a couple things as well as having Lexus look at it. They recommend I bring it to an auto electrician.
There are two scenarios: 1. I get three lights which makes the car go into limp mode or 2. I clear it or the third light (abs) goes away and the car drives normal and through all gears etc
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I've not worked on the car besides usual maintenance of changing the engine oil. Battery + connections good, only 2-3 years old
I haven't had this problem, although a quick online search indicates common reasons for a U0101 code are related to battery voltage, wiring/terminal damage, grounding, and other electrical/wiring issues. If I was in your shoes, I would start by swapping the battery from another vehicle if possible and seeing if the issue persists and/or getting the battery tested at a local battery shop. (How old is your battery?) After that I'd be checking the fusebox for any slightly loose fuses and checking under the hood for any bare wires. (Rodent chew damage, or rubbing and worn/contacting the bodywork) Y'know, the easy stuff you can get to yourself. If those don't eliminate the issue, my next step would probably be taking the dealers advice and getting an electrician to go over it, unless you've got a voltmeter, the wiring diagrams, and the time and patience.
Oxygen Sensor Output voltage (B2-S2)= 0.155V <------is this something to be worried about?
Oxygen Sensor Output voltage (B1-S2)= 0.855V
Oxygen Sensor voltage (B1-S1)= 3.246V
Oxygen Sensor voltage (B2-S1)= 3.241V
Oxygen Sensor Current (B1-S1)= -0.02mA
Oxygen Sensor Current (B2-S1)= -0.03mA
It fault codes seems to only appear for : ECU (#e8) = U0101 Lost Communication with TCM 1/2 & 2/2
No faults for ECU 2 (#e9)
Not something to be worried about. The S2 sensors only measure catalyst efficiency, so they could read anywhere depending on what the ECM is doing at the time. There is a random test sequence the ECM runs to measure catalyst efficiency, and you might have checked the voltage while that was in progress.
I haven't had this problem, although a quick online search indicates common reasons for a U0101 code are related to battery voltage, wiring/terminal damage, grounding, and other electrical/wiring issues. If I was in your shoes, I would start by swapping the battery from another vehicle if possible and seeing if the issue persists and/or getting the battery tested at a local battery shop. (How old is your battery?) After that I'd be checking the fusebox for any slightly loose fuses and checking under the hood for any bare wires. (Rodent chew damage, or rubbing and worn/contacting the bodywork) Y'know, the easy stuff you can get to yourself. If those don't eliminate the issue, my next step would probably be taking the dealers advice and getting an electrician to go over it, unless you've got a voltmeter, the wiring diagrams, and the time and patience.
Have you popped the cover on the ECM/TCU box and inspected the wiring and connectors? That's where I'd start. I'd also disconnect and reconnect the connectors on both units. It's a bit tedious as there are quite a few connectors, but if there is any corrosion built up on the pins, cycling the connections will often clear it up.
Do you happen to know where i can locate the fuse for the TCM or a wiring diagram TCM to ECU?
The only fuse box as per the fuse diagram that I can see relates to the transmission is the one below (15) which is located on the right side drivers side (AUS) panel. It's 7.5amps and looks to be good and not broken.
Have you popped the cover on the ECM/TCU box and inspected the wiring and connectors? That's where I'd start. I'd also disconnect and reconnect the connectors on both units. It's a bit tedious as there are quite a few connectors, but if there is any corrosion built up on the pins, cycling the connections will often clear it up.
If you have a blown fuse, you'll have a whole lot more DTCs than the one you have now.
Are you familiar with electronic systems troubleshooting? We're not looking for a fuse box. We're looking for the ECM and TCM box. It is rectangular from the top and has three 10mm head bolts holding the cover on. You need to remove those three bolts, and check the connectors under the cover.
I had a look at the box which houses the the ECM/TCM in the engine bay(3x10mm bolts) but have not attempted to unplug (afraid of breaking connectors/clips) but there doesn't seem to be any wires loose or corrosion so I decided to do the ECU reset by unplugging the 2 fuses in the engine bay. De-activated my parking sensors (don't know why but did notice one of my rear sensor is no longer flush with the rear bumper) and cleared the codes ( it allowed me this time). Started the car and no errors and drives fine (I hope) so will see if I get the error codes again in the morning. Would a loose wire from any other connections cause this?
I know the simple stuff when it comes to electronics but have the tools (multimeter/breaker box etc) but no skills in actual car electronic troubleshooting especially with these modern cars.
Appreciate the advice and it doesn't look to be a common issue with the ISF or any other Lexus models
I was able to get to the ECU and TCM. Wires look fine. Is there a check I can do on the module or wires? Cheers
Originally Posted by lobuxracer
If you have a blown fuse, you'll have a whole lot more DTCs than the one you have now.
Are you familiar with electronic systems troubleshooting? We're not looking for a fuse box. We're looking for the ECM and TCM box. It is rectangular from the top and has three 10mm head bolts holding the cover on. You need to remove those three bolts, and check the connectors under the cover.
Thanks Lobuxracer! Are you able to point out all the engine grounds or ones for ECM or TCM? While i have it out i might go ahead and check all grounds.
Originally Posted by lobuxracer
Not easily. At this point, I would reconnect everything and test.
Thanks Lobuxracer! Are you able to point out all the engine grounds or ones for ECM or TCM? While i have it out i might go ahead and check all grounds.
I don't have access to RHD wiring diagrams, so odds are even if I gave you what I have, it would be of limited help.
Still not luck, wires look ok from the ECM/TCM so plugged it all back, checked all wiring, fuses etc in the engine/interior. I have a week and a half to see if I can figure it out. My car is booked with tha auto electrician next week (only time they have available so gives me all this time)
I changed some fuses even though none were broken but now seems to be only have two lights (engine/traction) plus I can clear the codes even though it appears later in the day. I think it seems to work ok when the car is warm.
Whats your thoughts about grounding the TCM and ECM modules to the chassis? (chassis > tcm bolt > ecm) incase it's a grounding issue? Of coruse I'll be using correct terminals etc but is there a downside to grounding both modules? They are currently bolted to the plastic cover
Originally Posted by lobuxracer
I don't have access to RHD wiring diagrams, so odds are even if I gave you what I have, it would be of limited help.
If they work at all, the grounds are good. Lexus generally don't have grounding issues. Honda does mostly because they use a daisy chain methodology for grounding. Toyota/Lexus do not do this.
Is there a "how to" guide to remove the fuse box located in the engine for ISFs? I might go ahead and check all wiring underneath the fuses which links to the TCM. Looks complex and don't know where to start and don't wanna be breaking stuff incase there is a step-bystep guide.
Also, where is the CAN bus located for the ISF? Does anyone have a diagram or location details?
02-03-23, 01:25 PM
U0101: Lost Communication with TCM on ISF
