Hello guys, I own an AWD 07' IS250, I currently have these codes and the engine is not starting, car turns on with the display screen but that is about it.
I have ABS light on, Check Engine light on, and Battery light on. I Have used 3 new batteries, and even tried to jump-start the car.
List of Codes:
U0073: Control Module Communication Bus Off
U0126: Lost Communication with Steering Angle Sensor Module

 

Loss of communication as well as CANbus issues.

Other than checking fuses.... there really isn't anything you can do.

You're better off spending the bucks and pay the cost to have a professional shop diagnose the situation. I'm confident you're never going to locate the problem.

For what it's worth, the poser steering module is located underneath the battery tray.

I mean, I'm not saying you can't fix the problem.....I'm saying I seriously believe you don't have a chance in hell of LOCATING the problem, to fix.

 

Wow, okay that's even worse news than I was expecting, thank you though. Do you have an estimate of how much diagnosing/repair would be?

 

Diagnosis shouldn't cost more than $200......the independent shop I use charges $172.....the (Toyota) dealership I work at charges $260

I wasn't trying to be discouraging with my earlier comment, it's just that you need computer software to command modules to perform tasks while you monitor Real Time data. Some modules are "stand alone", some are peripherial while some are serial. There are so many modules associated with CANbus that anything you replace will be a wild guess......plus there are multiple CANbus circuits.

Regarding the power steering code......as mentioned earlier, the power steering module is located under the battery tray. Many Lexus cars have came into the dealership with that same code. I've repaired many vehicles with this code (been Toyota employee for 20+ years). This is what I've discovered:

The power steering module can become damaged due to (battery) acid vapors destroying the seal surrounding the PS module case. This allows moisture (rain water) to contaminate/corrupt the electronics within said module. It's very important to have a sealed battery in these cars.

Mice like to nest right there near the battery/steering module. Mice chew wires plugged into the PS module. Many times the problem was chewed wires, I don't know why mice choose this particular location to nest, maybe they smell the interior of the car and think it's a food source??? Maybe the heat from the exhaust manifold remains warm and mice select that location because it's hidden and heated? Don't know.

Those are the two main reasons I've found for the PS module failing. Inspect it.....maybe you'll get lucky and see some visual damage, repair/replace the damage.....maybe you'll even get luckier and discover that whatever damage the steering suffered is also responsible for disrupting the CANbus circuits. Kill two birds with one stone?

If I had your car in our service bay, first thing I would do is hook it up and run a bi-directional command/scan program. See what info it spits out. Obviously, I'd pull the PS module (since there's a code for it) and hook it up to a diagnostics tool capable of maxing-out it's operating perimeters. If any of its files are corrupted, I'd rewrite them into the map, if the module is damaged beyond being rewritable, I'd install a test module to see if power steering performance is restored. If the test module corrects the power steering issue, I'd submit a request to order a replacement module.

 

OP, if a battery went under voltage while cranking, this can and does force computers off line. When things drop off the communication bus (packet loss, data loss) unexpectedly, errors are thrown. This can easily create phantom errors that never appear with a good charging system and healthy battery.

I would be less concerned for now and focus on getting it running. When resolved/running, clear the errors and see what comes back.

What is the back story? How did it get to a condition of not starting? When is the last time it ran and what all has been done? More details please.

 

problem is that it wouldn't start up as soon as that code showed up, i didn't drive it for around 3 days or so and when I went to go start it up nothing would happen.

 

Can BUS can make your car not start right? Because as soon as that code appeared the car wouldn’t start up.

 

Yes. Bad CANbus can potentially cause the engine to not run.

CAN = Controller Area Network

bus = Data and control signals

Think of CANbus as an intersection where electrical information meets with other electrical information........this information is exchanged/combined and sent on its way to perform a task.

 

This helps. There are 4 different networks for data in these vehicles. If you have access to Techstream and Mongoose cable, you can test each computer and see which one doesn't respond. Then begin the deep dive of why? Any moisture in the cabin? Anything else change?

Any other repairs made, accidents, accessories added or removed?

 

Any water or moisture under your carpet on the driver's side?

Edit: steering angle sensor is built into the spiral cable (behind the steering wheel). I've seen an IS with a plugged moonroof drain cause water to run down the d/s a-pillar and into the junction blocks behind the driver's side kick panel. Water gets into the connectors and shorts and rusts them. The J2 connector for the steering angle sensor is there. Pink and White wires for the can bus for that system with a tiny white connector with 2 wires. If that's corroded or wet, clean it, etc. It may have also blown you MPX-B 10A fuse at the fuse block in front of the battery. I doubt your EPS ECU is faulty.