U1255 code in many Modules

1526 Views 17 Replies 4 Participants Last post by basscatt, Aug 19, 2019

Whamman

Discussion Starter · Jul 24, 2019

1998 Seville STS, 4.6 engine, 80k miles

I was passing a truck under heavy throttle and the engine died like I turned the key off.
Mountain road on a curve with no power steering and no power brakes...very hairy!

The DTC code U1255 "lost communications" shows on all of the following... DDM , DIM, IPC, RFA, RIM, VTD, MSM. The PCM had no codes. At the same time "service stability system" showed on dash.
The "lost communications" possible causes listed are...
-Loose control module connectors
-Faulty Control Module
-Control modules poor electrical connection
-Control Modules harness open or shorted

The engine will not start (no spark), and there is an electric humming from the back of engine (without key on) that is draining the battery.

Where do I start to solve this? Any help would be greatly appreciated!!

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basscatt

· #2 · Jul 24, 2019

Whamman said:
1998 Seville STS, 4.6 engine, 80k miles

I was passing a truck under heavy throttle and the engine died like I turned the key off.
Mountain road on a curve with no power steering and no power brakes...very hairy!

The DTC code U1255 "lost communications" shows on all of the following... DDM , DIM, IPC, RFA, RIM, VTD, MSM. The PCM had no codes. At the same time "service stability system" showed on dash.
The "lost communications" possible causes listed are...
-Loose control module connectors
-Faulty Control Module
-Control modules poor electrical connection
-Control Modules harness open or shorted

The engine will not start (no spark), and there is an electric humming from the back of engine (without key on) that is draining the battery.

Where do I start to solve this? Any help would be greatly appreciated!!

==============================
The DTC code U1255 "lost communications" ......................
the actual definition - there IS a difference -
U1255 - Class 2 Communication Malfunction (Serial Data Line Malfunction)

FIRST -
check the motor mounts -
I suspect that the front mount is broken -
thus allowing excessive engine movement - especially on acceleration -

and when you hammered the throttle - on a winding mountain road - passing a truck -
you tore some wires loose - broke a ground - etc -

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basscatt

· #5 · Jul 25, 2019

Whamman said:
Hi Basscatt
Here is something new... there is a small pump on top of the motor that pressurizes the injection that is running all the time until the battery is flat. This is with everything turned off. Any ideas?

====================
absolutely no idea what you are referring to

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basscatt

· #13 · Jul 26, 2019

I can't remember ever running across a fuel pump that constantly runs -
but that sure seems to be the issue -

check the fuse box under the back seat -

FUSE #1 is for the fuel pump - pull it and see if that stops the sound you hear under the hood -
if YES - plug the fuse back in

RELAY #39 is the fuel pump relay -
verify that the sound under the hood is still there -
then use the plastic handle of a screwdriver - or similar - and GENTLY tap on the relay -
if the sound stops - you found the problem - a stuck relay -
replace the relay -

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basscatt

· #18 · Aug 19, 2019

Whamman said:
Hello Basscatt,
Thank you so much for your help! You were right! The whole problem was caused by the motor mount breaking which caused a bad ground to the motor. The car sat in a shop for 2 1/2 weeks before anyone could work on it but was fixed with your help in 2 hrs!
You are The Master of Diagnostics!!

=========================
you are welcome - THIS is why we are all here -

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