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Our 2010 RAV4 is having an issue where the 4WD, VSC and ABS lights come on nearly every time we drive the car. Toyota ran diagnostics on the car and found the following codes: P1578, U0073 and U0126. Their diagnosis is that the steering angle sensor module is not communicating with the 4WD ECU. They recommended starting with 3 hours to troubleshoot the pin connections on the 'can line connections'. The mechanic said this will cost several hundred dollars and that is might not even uncover the issue.

I am looking to troubleshoot this myself since I am mechanically inclined; however I am looking for a diagram that shows all of the locations of the various ECU's in our car. I have found the 2-3 ECU's behind the glove box that all appear to be for the ABS system.

Thanks in advance!
 

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What we've seem over the years is that one failure, as in a bad wheel speed sensor, may set many apparently unrelated codes. And I'm sure some dealers use them to sell unnecessary parts and repairs. I always recommend resetting all codes and seeing which one comes back first before trying to trace out all of them.
That brings up two questions. Who read the codes and were they reset before the diagnosis you listed was made?
BTW, two of the ECUs behind the glove box are for TPMS and 4WD.
 

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Discussion Starter #4
What we've seem over the years is that one failure, as in a bad wheel speed sensor, may set many apparently unrelated codes. And I'm sure some dealers use them to sell unnecessary parts and repairs. I always recommend resetting all codes and seeing which one comes back first before trying to trace out all of them.
That brings up two questions. Who read the codes and were they reset before the diagnosis you listed was made?
BTW, two of the ECUs behind the glove box are for TPMS and 4WD.
Thanks for the reply. I have reset both the ECU codes (pulled EFI Main fuse) and well as the Body Control codes (PIN's jumped and pressed brake pedal until cleared). I verified all codes were cleared by the rapid flashing of the lights on the dash (no codes flashing).

Once cleared, the same codes return and the same 3 lights always trigger (ABS, 4WD and VSC). They come on about 80% of the time we drive the car and trigger randomly during the drive. Sometimes early on and sometimes after 10-20 minutes of driving.
 

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Okay, good info.
Since the MIL (CE) light isn't on the jumper/brake method should clear all the codes w/o removing the fuse. You might try that to find out.
You've probably looked up the codes (I haven't) please list them.
 

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Okay, good info.
Since the MIL (CE) light isn't on the jumper/brake method should clear all the codes w/o removing the fuse. You might try that to find out.
You've probably looked up the codes (I haven't) please list them.
I used the 'jumper/brake pedal' method to clear the ABS, 4WD and VSC codes. I had to use to remove the fuse to clear the cruise control code that triggers from the other codes.

Here are the codes I find every time (based on # of flashes with jumper pins):
1) VSC 43 and 63
2) ABS 94
3) 4WD 84
4) Cruise Control 69

Here are the codes Toyota found (based on their diagnostics):
1) P1578
2) U0073
3) U0126
 

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I was hoping this was something fairly simple like a rear wheel speed sensor like I had on mine twice. I ended up replacing both sensors and no codes since.
But not the case here. Your codes are CAN communication system related. I don't know how it works for sure but seems to me that any of the ECUs on the CAN bus could be causing it or it could be a wiring failure but unless the car has had major trauma that's unlikely.
In any case you'll definitely need the factory repair manual to make any headway. I have it on CD but hopefully you and JuneBug can get his links working.
 

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Discussion Starter #8
I was hoping this was something fairly simple like a rear wheel speed sensor like I had on mine twice. I ended up replacing both sensors and no codes since.
But not the case here. Your codes are CAN communication system related. I don't know how it works for sure but seems to me that any of the ECUs on the CAN bus could be causing it or it could be a wiring failure but unless the car has had major trauma that's unlikely.
In any case you'll definitely need the factory repair manual to make any headway. I have it on CD but hopefully you and JuneBug can get his links working.
Only mod on the car that is wiring related is a remote start that we installed 2+ years ago. The remote start works perfectly, but I'm wondering if its causing some sort of issue that is triggering these codes. The code issue has been going on for a couple months.

I have not heard anything from Junebug on getting the factory manuals :(
 

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The remote starter may be at fault since it will also be connected to the CANBUS system. Anything that is connected to the CanBus network should only communicate when it needs to. If the remote starter module is constantly "hocking" the network, it will prevent all the other ECU from communicating on it as well. CANBUS network is a shared 2 wires network. Try locating the remote start control module and also the immobilizer bypass module. Trace the wire that is connected to the CANBUS network ( usual connection place will be right by the DLC-3 connector. That would be the plug when you plug your diagnostic reader into. Disconnecting those wire will allow you to narrow down the problem.
 
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