Intermittent "cannot communicnate fault" (U0155) on brand X car.  - Page 1
Forum section: electronics / repair

author: AnneRanch
author_rank: Contributor
timestamp: September 17, 2019, 03:38:14 pm
content: Same "disclaimer " as posted elsewhere.If this is WRONG place to post this, please ignore it.I have annoying , intermittent , problem with loosing communication with car instrument clusters.Both speedometer and tachometer, separate instruments , loose "communication" and code (U0155) is posted to the monitoring electronics.The "results" are multiple - but the main one is "check engine soon".The code can be erased, reset - and everything will go back to normal - no problem.I have replaced the "speedometer" cluster and make sure ALL connectors are "locked".Here is the weird part.It mostly happen on initial start....I can operate "door lock switch" and after SEVERAL tries all goes back to semi-normal - but the "check engine" needs to be reset.SOMETIME I can open and shut drivers door (!) and everything goes back to normal. Again - the system codes needs to be reset.Restarting the car SOMETIME clears the panels, but the "check engine" needs to be reset.Mrs Google indicates this s common problem and that "you are missing ground" !I have been thru ALL electrical parts and cannot see any questionable , loose electrical problems.The mechanic checked battery and generator - no problema.I am open to suggestions, however, my only option is to fix it myself - several "mechanics" where unable to offer solution.Seems "intermittent U0155" OBD code is "over their heads".Cheers

author: SMdude
author_rank: Frequent Contributor
timestamp: September 17, 2019, 10:49:00 pm
content: If it only happens on startup, I would suspect that you may be getting a voltage drop that is too low for the controllers to continue to operate properly and weird stuff can happen.What I would be doing is getting an oscilloscope and checking the voltages at battery and supply to your controllers while cranking and see what voltages drop to what.Also the communication bus can be checked with the scope as well as there could also be interference, or a problem there.A really good auto-electrician should be able to diagnose and repair it.

author: AnneRanch
author_rank: Contributor
timestamp: September 18, 2019, 12:25:18 am
content: All good points.Not to muddy the waters...Why does it "recovers" when the opposite is happening - locking ALL doors electrically could generate drop and if the coils have faulty diodes it would also generate spike.BUT - the engine is running , hence generator is working when that is happening.Sorry, my Tek scope is broken...

author: SMdude
author_rank: Frequent Contributor
timestamp: September 18, 2019, 11:05:12 pm
content: It could be something like a main supply connector has a bad connection(loose contact, corrosion, been hot) which then when you get a high demand for current(4x door solenoids instantaneously drawing a gulp of current) that can be enough to cause a significant voltage drop.Check fuse contacts and check/swap relays of the same type around.A lot of the time we think bad earth, but many times, it is bad power.

author: maginnovision
author_rank: Super Contributor
timestamp: September 19, 2019, 12:30:06 am
content: It would help to know what car it is. Seriously.

author: coromonadalix
author_rank: Super Contributor
timestamp: September 19, 2019, 12:37:53 am
content: this error ?https://www.troublecodes.net/ucodes/u0155/

author: Chris56000
author_rank: Frequent Contributor
timestamp: September 22, 2019, 07:50:33 pm
content: Hi!If the car is a Ford then there's two well known causes of dash cluster problems:-1) High resistance or corroded earth connections bolted to the bulkhead behind the dashboard cluster - some of the instrument earth-return circuits are bolted here;2) The lead-free muck used to solder all the components/ICs on the instrument-cluster itself deteriorates!Chris Williams

author: pbarton
author_rank: Frequent Contributor
timestamp: September 23, 2019, 09:30:18 am
content: As this happens mainly "on initial start...."You also need to check the integrity of the starter circuit. Including battery terminals, battery to chassis bonding, chassis to engine block bonding, starter to solenoid bonding, etc. Remove the straps and clean the surfaces, tighten up those nuts. The instrument cluster requires the engine block to be at chassis ground potential.Why does the "door lock switch" clear the fault? I think that you may have a bad battery bonding fault and the bonding impedance is somewhat unstable.

author: AnneRanch
author_rank: Contributor
timestamp: September 25, 2019, 04:19:17 pm
content: Thanks for all replies.This "problem" initial failure was with ENGINE running , and car moving...Both (Honda 2007) instrument clusters - speedometer ( 0 speed !) , and tachometer ( 0 RPM!) plus other NOT normal lights failed.After taking the dash apart, noticed LOOSE speedometer cable and replaced speedometer cluster.Same problem.Checked ALL obvious ground and battery connections. Cleaned them!.Still fails.Checked SOME fuses , reinstalled !Still fails.Ready to replace almost out of warranty battery.If it is bad ground or battery connection - I have run out of places to check.My next step will be toturn headlights on highrun ACrun AC fanAKAput a load on the system when starting the engine and see what happens....I NEED to find the OTHER end of the "communication harness".I am out of ideas.

author: narkeleptk
author_rank: Contributor
timestamp: September 26, 2019, 02:42:49 am
content: Does the cluster completely loose power when it happens or does it just stop responding (lights still on)?I've seen some pilots around that year have issue's on the can lines that cause this problem, nothing to do with power. What module are you getting the "lost communication" code in the ECU, BCM, Radio, SRS, etc, all of them or just one of them? The code does not indicate you have a problem with your cluster at all, it simply means the module you pulled code from (i assume ecu) has lost communication with the it.You say you want to know the other end of the harness.... Well It goes all over the place. You have some wires going to the switches, some going to ecu and others going else where. If you would provide your Year/Make/Model then I or someone else probably could have provided you wiring diagrams.

author: maginnovision
author_rank: Super Contributor
timestamp: September 26, 2019, 04:22:41 am
content: 2007 Honda what?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 26, 2019, 04:43:20 am
content: When you pull several dozen amps or more from the battery and through the starter current splashes everywhere. I am not familiar with your year Honda, but every vehicle I have ever worked on has many ground bonds. Some at the back of the block. Some in the passenger compartment. Some at various fuze panels. Some between various body components. Knowing how attentive car manufacturers are to costs you know that they are not frivolous. If one or more of these bonds is not good some portion of the electrical system gets a roller coaster ride relative to the rest of the system and all sorts of mayhem results. It is probably worth getting access to the service manual and interpreting the wonky schematics to find where bonds are supposed to be and verify that you have indeed checked all of them. The manuals for the cars I currently own actually have full multi-page schematics dedicated just to power and ground systems.

author: maginnovision
author_rank: Super Contributor
timestamp: September 26, 2019, 04:47:51 am
content: If he tells me what the car is, preferably including engine option, I can give him a complete list of every related ground and their connection points.

author: AnneRanch
author_rank: Contributor
timestamp: September 26, 2019, 02:37:03 pm
content: I really appreciate all the comments, it is very helpful.2007 Honda Civic - 4 door.I am not sure HOW to identify "model" .Should it be part of WIN?A list of ground points would be nice.I do have a Haynes manual , but was unable to find such list or actual battery / ground connection and "the other end)of the harness'' from instrument cluster ( tachometer) to the "sender".The harness ends at "speedometer" and from there goes to "tachometer" then .... where ?I have NOT replaced the tachometer cluster, only the speedometer.I interpret U0155 as "failure to communicate" WITH instruments clusters and that is a real indicator of the failure.Both clusters stay ON, AKA having power. Just do not function as normal.For example "hand brake" light comes on, so does ABS.This may be irrelevant, but AC also quits when I get U0155 code.

author: maginnovision
author_rank: Super Contributor
timestamp: September 26, 2019, 05:31:16 pm
content: I'll get back to you later today when I get back to my desktop. Which trim level is your vehicle(SI, dx, ex, lx), Auto/Manual? Or you can just give me your VIN.

author: maginnovision
author_rank: Super Contributor
timestamp: September 26, 2019, 06:12:30 pm
content: I've attached the ground location for the speedo which is G504. The other ground for tach is G503, also attached. The comm line for the speedo is just a uart line, pin 20 or 2 on tach, depending on exact model. Or on the speedo pin 7 or 1. (DX is 20/7, all others are 2/1). Attached schematics for tach and speedo. I also attached description for U0155 fault and diagnosis procedure for the fault with associated images. I don't have any time to go through it to give any suggestions right now so respond back if you have anymore questions.Quick edit: None of this may apply if you have an SI(like me), I didn't check differences.

author: Lorenzo_1
author_rank: Regular Contributor
timestamp: September 27, 2019, 05:02:58 am
content: A couple of other suggestions for you based on a recent comms failure and several warning lights in a Discovery 3. It took many hours to resolve. I have a very good mechanic who couldn't pin it down after spending hours on it - he didn't charge me. He pinned it down to something awry in the stop light circuit that wasn't fixed by replacing stop/brake pedal switch. Thought it might be bad ABS ECU. Eventual self-help solution required careful analysis of wiring diagram to work out signal paths to and from pedal switch, CRO to examine signals at pedal switch and ABS ECU and tone generator/probe for circuit tracing.CRO helped identify normal and abnormal signals in and out of ABS module and pointed to a break in one signal wire. Tone generator and probe used to trace for good/bad connections from ABS connector and stop switch circuit to various points in car. This allows you to inject tone at one end of vehicle and detect which of dozens of wires it appears (or fails to appear) on - even when they're well buried in wiring looms. In may case two signal lines to ABS module had been chewed by a rat - one broken and one holding with only a single Cu strand. Both were buried deep behind main fuse board in pax footwell and would have been very hard to find without tone generator because of surgery required to access them. Fix cost me 20c.Be careful with tone generators as some ECU/control modules may not like voltage signal applied. I was conservative and disconnected ECU and ABS module during tone tracing.One Youtube video () for U0155 fault on Honda Civic shows use of a CRO to identify no comms and excess voltage on CAN line and further diagnosis by disconnecting ABS module which brought back comms and fixed dash functions. Put down to fault/short in ABS module. Bad grounds are a common source of failure and a good starting point, but you might need to cast your gaze a bit wider. Hope this helps.

author: AnneRanch
author_rank: Contributor
timestamp: September 27, 2019, 01:31:55 pm
content: Thanks, this is very helpful and I appreciate you spending time on it.Unfortunately the video identifies faulty ABS something ( module ?) .What I have is an intermittent problem.As soon as it quits raining I'll take a look at the ground points.I'll check if I can rent a OBD scope, but that may be useless since I already know I have a U0155 and ONLY U0155 fault.Thanks

author: maginnovision
author_rank: Super Contributor
timestamp: September 27, 2019, 04:29:31 pm
content: Since it's an intermittent fault and you have no other faults you're likely looking for a wiring/connector issue. Even though you have no other faults it might not be a bad idea to do the simple resistance and continuity checks if the ground connections are ok. The ECU and wiring harness are under the hood and if you have help it might be good to have someone try and wiggle and shake the harness. You should see 0 change in your readings. It's USUALLY not any issue deep in the harness rather it's closer to connectors since that's where they aren't wrapped and tied down. Also verify that all 3 under hood ground straps are connected properly and clean. Has the car ever been in an accident? Sometimes body shops aren't as careful with a wiring harness as they should be and you can see problems occur far enough down the line that you don't think to connect the two events.If you need anymore data just ask, good luck with the repair.

author: muzaffar84
author_rank: Newbie
timestamp: April 15, 2023, 12:56:09 pm
content: @AnneRanch Did you manage to solve your problem? I have exact same issue in Honda Civic 2011. intermittently getting check engine light on and when this happens, AC trips, ABC light turn on, speed and rpm reads zero. Everything goes back to normal after few seconds except the AC (for AC I need to turn off and on the vehicle). Code is always U0155 only (tried various scanners). So far disconnected and cleaned IPC connector and 3 PCM connectors but problem is still there. Any help shall be highly appreciated.