Ok, my wife's 2011 Pilot EXL is having trouble. The outside temp reading is ---. I replaced the sensor but that did not fix it (hoping for a $20 fix - should have known better). The AC does not turn on and the driver side door lock does not work or works intermittently, mostly not. Scan tool gives me some codes: U0155 - MICU cannot communicate with gauge module; U0199 - MICU cannot communicate with power window master switch; B1275 - Headlight OFF position malfunction; B1277 - Headlight AUTO position circuit malfunction.

The latter two B codes were not present originally, but have since surfaced while I have been trying to troubleshoot.

I have a 2009-10 shop manual and have been trying to troubleshoot the B-CAN bus but have not been successful in pinpointing trouble. My scan tool has some functionality that allows me to see that the MICU is communicating with the B-CAN bus but nothing else is. All other systems show "not available". Some items are not installed in my car, but others are and should be available, like the gauges, of course. When I do the self-diagnostic procedure on the gauges I get an error 2 in the window on the instrument panel. This points to the BCAN bus, according to the shop manual. So, something is rotten somewhere.

I would rather avoid taking to the dealer as they will want to charge me thousands to replace the MICU and the door control unit, and who knows what else. My sense is that the B-CAN bus has a problem somewhere, but I am a bit lost as to how to approach this logically. The shop manual jumps around a lot and I cannot quite get my mind around the procedure and logic involved.

Also the shop manual assumes you have access to the Honda software tools which I do not have. I can see a lot with my Top Scan gizmo, but not everything. It allows me to test the fan motor and the AC clutch which are working fine. The problem appears to be somewhere in the comm bus and one or more controllers.

I am about to start taking the dash apart to get at the interior fuse/relay box and try some of the continuity tests with the door but I really hate to start ripping things apart without a strategy for how to assure I'll make progress in diagnosing the issues.

One other thing, it occurred to me that the battery could be the culprit and this one is about 3.5 years old (10/21 sticker on it), but it seems to be ok. I did a poor man's load test with a DVM, and I am seeing no less than about 10.5 volts during the brief startup dip. No evidence of any bad cells as it seems ok at about 12.5V. I will put on charger tonight and see where we are in the AM. Probably worth taking it to have a parts store test it. But the voltage appears high enough to not be the cause of a continual blank temp reading or the door lock issue. But, what do I know? Maybe I am not understanding something here. [Since it is my wife's car, I probably will get a new battery soon as I don't want her stranded or to have any chance of becoming stranded. So, I'll get it tested and go from there.]

Any suggestions, thoughts, advice would be greatly appreciated.

Thank you.

 

Take it to an established shop.
Any of the iATN shops can fix this for you for a fair price,

https://iatn.net/repair/?

 

Thank you for the suggestion.

As a follow up, I believe the battery is ok. It charges to 12.6v and holds it.

However, I have now gotten myself into the deep end. I disconnected the various connectors to the MICU/fuse/relay box, and performed various continuity tests per the shop manual. All tests passed. So, I reassembled the MICU with its many connectors. Put the key into the car and now I have nothing. The gauges are dead except the fast beeper telling me the key is in the ignition, and the gauge night illumination lights at the top of the gauge panel are lit. The interior lights work, so there is power to the car, but nothing functional works like door locks, the radio, etc. Weird. Getting 12v at pin 16 on OBD connector, but 1.5MV at CAN Low and CAN High. Almost 0V but not quite. 53-54 ohms across the same two CAN pins, so that should be in the acceptable range for the ideal 60 ohm reading on the B-CAN.

Looks like I'll have to get it towed to the shop and hope for the best. Very strange. I did nothing except disconnect and reconnect a bunch of connectors following the shop manual procedures. I double checked the connectors and inspected all of the pins and sockets for damage, but all looks fine. Also, a bent pin or two should not shut down the entire vehicle unless extremely unlucky pins combination is damaged.

I am tempted to replace the MICU unit, but since it could also be the guages and since both of these need reprogramming when replaced, as I understand it, I guess I'll have to cry uncle this time. I have done countless repairs of increasing difficulty to this car and my other cars over 30+ years. This is a new one. I am completely scratching my head.

Will let you know what happens just in case someone else ever encounters this issue.

For the record, I am betting it is the MICU unit. Let's see if that turns out to be right. Looking to salvage some dignity here .

 

Unless you load test those circuits you can't be sure it's not still bad. Many high resistance shorts will not be found by a resistance test. When they have current flowing through them the resistance gets hot and becomes a problem. Your meter does not load the circuit with enough energy to expose the problem. With load testing you are looking at voltage. A drop in voltage and there's resistance in the line. Easy to find if you know what you are doing and have good diagrams.You may find a jobber who does this mobile. Those who do know what they are doing. You can expect to pay 120/hr.

 

Understood and agree. I was just looking for something to get my bearings. I am pretty sure that there is no power getting to the gauges through the ignition switch circuit followed by the MICU/fuse box. But there is no voltage showing up on the gauge connector at pin 32. The non-switched circuit is getting battery voltage at the gauge connector pin 16 and I believe that is what is causing the key-in-switch beeper and the ambient lighting for the dead gauges to work. I believe the ignition switch is ok but I am not yet completely ruling that out. If I can confirm it is ok (need to find the test in the shop manual), then it would appear to be the MICU/fuse box or the gauges, or both.

 

Well, it turns out the mechanic working on this car is more than a bit dense and should be summarily fired.

I was able to isolate the loss of power to the gauges by performing the ignition switch test from the shop manual. The ignition switch tested fine. But then I looked at the schematic and saw that the path from the battery to the gauges went from the master fuse in the engine bay to the ignition switch to fuse #10 under the dash and then to the gauge connector pin 32. So I tested continuity from the ignition switch to the gauge pin 32 - nothing. Next I tested from the gauge pin 32 to fuse 10 - continuity present. Finally I tested from the ignition switch to fuse 10 - nothing. So, the problem had to be between fuse 10 and the ignition switch, specifically the pink wire that should connect them. I visually traced the pink wire from the ignition switch up into the top part off the dash where the driver sits. As the wiring harness disappeared upward, I was having trouble seeing it because there were two connectors blocking my line of sight. I saw those connectors multiple times while trying to verify my reassembly of the MICU/fuse box. Each time I was sure they were connected together and so ignored them. Well, there were not. Instead, one of them had the pink wire running to it. And neither of them was connected to anything. Then I remembered that the very first connectors I unplugged were getting in my way so I stashed them up in the dash as high as I could push them. They never got reconnected. What a humiliation! But also what a relief!

Once I reconnected those two connectors, she came back to life and now I am back to having just the original problem of no outside temp reading, no driver power door lock switch response, and no AC activation. Back on the gravy train as it were. .

The bad news is this was all self inflicted. The good news is that I finally developed a structured process for hunting it down, and the only cost so far is my time, no dollars.

Now with renewed vigor I will figure out what to do next.

 

You ought to learn how to load test. It finds the hard ones that a meter alone will miss.

 

I am sure you are correct. Any new troubleshooting skills when it comes to auto electronics can only help. At this point I am convinced it is most likely the MICU, next would be the gauges, and then there is small chance it is the driver door master module.

I have purchased a new Chinese knock-ff door module for $30 on Amazon, plus a used MICU on eBay for $100 that is guaranteed to work or be returned. If these do not solve the problem, then I have found a mail-in service that will take my gauge cluster and transfer the info to a working used cluster for about $350, and return both units to me.

So, to buy these parts new would cost $2,500-$3,000 plus labor to diagnose, reprogram, etc. Using my approach, depending on which unit is bad, I will pay $30 to ~$400 max since I can return the Amazon item and ship the eBay item back. Or I can keep them all and still be way ahead.

I would bet the dealer would take me on the wild goose chase of replacing each component one by one.

Still may have missed it, and none of these components fixes the issue, we'll see.

 

Save your old stuff as you may find the new is no good.

 

Yup. Will do. I never toss anything until at least a couple week or a month after the replacement has been working reliably. I saved a bad alternator for 10 years once and then when the replacement went bad during a long warranty, like 10 years or lifetime, I got a full refund, figured out how to rebuild the OEM Bosch alternator (just needed new brushes) and it has been working flawlessly since then. Sometimes you get lucky.