Fault Code U0401-64 - Signal Plausibility Failure ECU->TCM

[Michael Conley]

So after sending my LR4 to the dealer to diagnose the problem I'm having here, They determined after about a week that it was the fuel injectors misfiring/weak spray on one bank (1,3,5,7).

In the process of getting a quote, I found an indy who though this was odd, especially since its unusual for an entire bank to go and that 5 of my emissions monitors are not ready, preventing me from getting inspected.

He had me come down so he could run some diagnostic and after some time he uncovers:

• There are no misfires (*** dealership)
• The fuel system monitor should be one of the emissions monitors that should immediately gets ready the minute the car starts, which it this case, it's not.
• Fault code U0401-64 which indicates that the TCM isn't getting any data from the ECU.

In his experience he would find it strange that the ECU would be something which would need replacement so we're both digging around the web to see what we can find.

Anyone run into this? Thinking a place to start would be to check the wiring between the ECU and the TCM.

Thanks

 

[Michael Conley]

Kindly bumping as any help is appreciated

Anyone dealt with their fuel system monitor not kicking in?

Further digging into the workshop manual recommends that I look a little more into any codes thrown by the ECU which requires a return to the indy as I don't have gear like that.


Thanks

 

[jlglr4]

The problem started with hesitation under hard acceleration. The prior post goes on to look at transmission problems. If it’s hard shifting (or failure to shift), that would suggest transmission problems, but hesitation under hard acceleration sounds to me more like hard misfiring.

Very odd that the indy did not detect misfires, and the dealer did. Did your indy run the engine hard to look for the misfires? Some problems will only lead to misfires under hard acceleration, not at idle or light acceleration. If the dealer spotted misfires, and given the symptoms, I’d tend to think the engine is misfiring.

The indy came up with a U-code, which is a communications failure, but seems odd to me that you’d get this kind of drivability issue from a com failure to the TCM (transmission control) without some kind of hardware failure as well (P-codes).

Looking back at the dealer’s diagnosis - misfires all on one side of the engine - that sounds like it would give you the hesitation (bucking) you were experiencing. All on one side of the engine might suggest a fuel delivery issue to that bank (each bank has it’s own high pressure fuel pump), or maybe clogged catalytic converter on one side (as you hit those high RPMs, the backpressure from a clogged converter might be causing some problems). Could also be an O2 sensor on that side.

Fuel injectors - it is a bit coincidental that all your fuel injectors would go bad on one side of the engine first, but could be that they’re all going bad on both sides, just the one side showing up first. Still, seems odd.

The fuel system monitor readiness is a mystery, as is the failure to through any codes. I wonder if the PCM needs to be reflashed.

If you had a GAP tool, you could take a look at a number of these things, but I assume you do not have one. Might be worth buying one in this case.

Hopefully someone with more knowledge/experience can chime in.

 

[jlglr4]

Just saw a post on another forum re fuel system ready. Problem required a PCM reflash.
https://landroverforums.com/forum/lr4-38/emission-monitor-fuel-system-not-ready-103325/

 

[Michael Conley]

Just saw a post on another forum re fuel system ready. Problem required a PCM reflash.
https://landroverforums.com/forum/lr4-38/emission-monitor-fuel-system-not-ready-103325/

Yeah, hopefully the same will work for me, will let everyone know how it works out. I ended up getting a GAP tool but I'm wondering if I should just leave it to the pro to re-flash. Not too keen on potentially bricking my truck

 

[jlglr4]

Wish I could give you some reassurance, but haven’t done it myself. Have heard the GAP team is good with support though. You could start a new thread - see if anyone has experience reflashing from the tool.