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Codes U0100 and U0101 lost communication

Tiny
CHRISTA DICKSON
  • MEMBER
  • 2003 MAZDA 6
  • 4 CYL
  • 194,524 MILES
Okay, so I bought this car not even a week ago and it has been driving okay. Until last night. It loses a lot of power and is now pulling codes u0101 says lost communication with TCM and code u0100 lost communication with ECM/PCM A. U0155. I'm not sure if it's at all related but the gear shifter has been getting stuck sometimes as well. I'm not sure what needs to be addressed here or replaced to fix problem, but it's driving really bad and I hope it's not a big deal. Opinions on cause if this appreciated. Thanks
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Wednesday, June 10th, 2020 AT 1:36 PM

10 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,665 POSTS
Hello,

Lets test the main power and ETC relays. here is a guide to help and we should check the sues as well. Here is the wiring diagrams for the main power and the relay and fuse locations below:

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

and

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Check out the diagrams (below). Please let us know what happens.
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Thursday, June 11th, 2020 AT 11:58 AM
Tiny
CHRISTA DICKSON
  • MEMBER
  • 141 POSTS
Okay, I will do that and let you know. You said we should check the fuses as well? I'm not sure I know what your talking about. Did you mean the buses? Or clarification please and thanks. I will update this evening on the fuses and relays.
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Thursday, June 11th, 2020 AT 2:48 PM
Tiny
CHRISTA DICKSON
  • MEMBER
  • 141 POSTS
Sorry had a brain misfire moment there. You meant the fuses right? They all check out good and the relays. Upon inspection I came across a sensor mounted behind battery with what looked like a cut hose at the bottom, typed in number and it says it MAP sensor. Is that hose supposed to be connected to something and if so where does it go?
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Thursday, June 11th, 2020 AT 11:09 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,665 POSTS
Yes it is suppose to be connected, but it will not cause the communication faults. If all fuses and relays are good lets check the system grounds next. The u0101 code is telling us the TCM is bad. Here is the location so you can try a used/rebuilt unit. Check out the diagrams (below). Please let us know what happens.
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Friday, June 12th, 2020 AT 10:11 AM
Tiny
CHRISTA DICKSON
  • MEMBER
  • 141 POSTS
Okay, I went to pick n pull (salvage yard ) today and got a TCM and ECM. It seems like the TCM to me its shifting hard and not wanting to go into correct gears and has even got stuck in to high of a gear when on hwy. So I'm going to start with that. Is there anything I need to remember? Or does the ECM need to be programmed to the car to work? I'm installing tonight I'll let you know what happens.
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Thursday, June 18th, 2020 AT 3:12 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,665 POSTS
The TCM may or may not need to be programmed I would install it to see what happens. Please let us know.
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Friday, June 19th, 2020 AT 10:01 AM
Tiny
CHRISTA DICKSON
  • MEMBER
  • 141 POSTS
I did and it was actually worse.I got stranded in the middle of intersection twice after having to come to a complete stop and car wouldn't move. Rpm's wouldn't even rise.I ended up putting it in neutral getting rpm's up to around 4,000 and slamming it into drive to get it moving and home. Everything I have read everywhere is saying the TCM is plug and play on my car but it's my first Mazda so learning as I go. I did get it used so I guess there's a chance it was bad but ended up putting old one back on because it does at least move then. Stumped on what to do next. Please advise. Thanks
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Sunday, June 21st, 2020 AT 4:07 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,665 POSTS
That is the problem with communication errors, the ECM also is in the CAN which could be causing the problem as well. The next step would be a used/rebuilt ECM also I would clean the throttle body as well. here is a guide to help you and the ECM location and replacement instructions:

https://www.2carpros.com/articles/throttle-actuator-service

How does the wring look has there been any damage or repairs made? Check out the diagrams (below). Please let us know what happens.
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Tuesday, June 23rd, 2020 AT 11:39 AM
Tiny
CHRISTA DICKSON
  • MEMBER
  • 141 POSTS
Okay, I at least got the car driveable the third TCM I got from junk yard got the transmission driving normal finally. I also fixed the ignition coil. Car was good for 2-3 days no check engine light then yesterday it started pulling u 0101 and u 0155 again but it's still drivable and not tripping or driving horrible like it was. I hope it stays that way. I grabbed a extra ECU from junk yard. Could that be causing the issues? I have to get it programmed. And would like to know cheapest way to do that.
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Friday, June 26th, 2020 AT 5:01 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,665 POSTS
Good job getting the used ECM. some cars you can plug and play the ECM. we have a new CAN video you can check out.

https://youtu.be/InIlnsjOVFA

Sometimes it can take the car getting through the relearn process before everything goes back to normal. Was the car jump started backwards by chance?
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Sunday, June 28th, 2020 AT 11:01 AM

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