No Lock and Unlock from Key Fob
Subaru seems to be the last car line to show up with data on the information sites. This one was no different. I was called to a body shop that had just done some work on the back end of the vehicle. After the repair, the lock and unlock did not work.
First task was to Check the Fob. I used the TPMS tool and tested it. All OK. I scanned the vehicle and no codes showed up. Tried to reprogram key. Fail! Hmmm.
I pulled up two diagrams from the site I use and neither was exactly the same. This vehicle had a bladed key. It was not a Hybrid. I found with a bladed key and Hybrid and with proximity key with or without Hybrid. Since the problem started after the repair I pulled the panels to look for any disconnected wires. I did not find anything disconnected. I did find the keyless access and TPMS module. The module picks up the signal from the key Fob and the TPMS sensors.
I decided to be creative and see if I could see the air pressure if I tripped the TPMS sensors. I hit all four with my TPMS tool. I came back to the computer display and the pressures showed up where they were blank before. I surmised that the module must be working. At this point I was scratching my head. The TPMS sensors were being recognized but not the key Fob.
I asked the customer and they told me that they had cleared the codes before my arrival. There was some sort of code about communication. I decided to scan the vehicle again as there were multiple key cycles since the first scan. Sure enough. There was a code, U1500. I Googled the code and found that it was a code for the communication line to the BCM. There was also a TSB with a simplified wiring diagram. Without the module connected, I was able to get a nice square wave signal from the BCM. (UART signal from BCM) While I was there, I checked the powers and grounds. I had the switched ign 12v and GND but no B+. The google diagram had the correct positions for the wires. It also had a fuse position. I looked and #4 fuse was blown. Doh! I replaced the fuse and verified the repair. Now the locks work with the key Fob.
So here is the take away..
Some misdirection due to the vehicle history and codes were cleared. (Code would have helped find the correct diagram in the first place)
Did not have a good print, so I improvised.
Could have looked in the owners manual for fuses, maybe something would have stuck out. (Not near as much fun as the long way)
Got hung up on the fact that the TPMS would register but not the Fob. I was ready to condemn the module. (Damaged from welding in area?)
The reason the TPMS worked is because the key was on powering the module. With the key out, the module was dead without the B+
So not a perfect flow of diagnostics. At the end of the day the problem was found.
Good job Mike! I wanted to start a new question about testing keys/fobs, However, you mentioned something here about that. So, I will just ask you directly, what is a good way of testing keys and or fobs? They could be bladed old school kind of keys with a chip in them or new fob style keys... how can one reliably tell if the key is able to produce a good signal? Also the wireless transmission
Hi Maynard, The Bartec 400Pro has some excellent features for fobs and proximity keys. Chip keys can be tested with tools like the Zed Bull. Some of the new keys are not covered by the "clone" tools. Tools like the key tester loop will give you an indication if the key coil is signaling the key and if the key responds. ebay.com/itm/2018-OBD2…
As far as testing fobs, you can purchase key fob testers there are many different kinds. Most will not work on the 900 MHz range so beware. You need specifics for say a 2018 ford prox remote button test, They run in that range. So just because my tester shows a signal from the remote does not mean the module on the car received and processed, Meaning, you can think you have a good battery and
Mike, thanks for the case study and showing the use of the SteelmanPro scope. Unfortunately, very little information about it on the internet, I can't even locate it on the manufacturer's website. Any pointers?
I missed that they even made one. Good eyes Dmitriy. Found a seller on ebay; ebay.com/itm/STEELMAN-7…
Dmitriy, I helped develop the kit for Steelman when I was working for the company. The DSO is good for quick testing of a single signal. I like that it has a rechargeable battery. It is frustrating trying to find a 9V when you need it. The fuse for current flow measurement is not common. It may be good to buy a few fuses to have on hand. I don't have my notes anymore so I can't tell you exactly
Mike, thank you for the spec sheet. I have added the scopemeter to my compilation: diag.net/msg/m2e5v8z1vo… and it does look quite attractive! Your specs say PC Interface: Bluetooth, while the ones on eBay say: USB. Are there a few versions floating around? What do you expect the price for the newest version of the unit to be? And I wonder where eBay sellers get the item to
"I asked the customer and they told me that they had cleared the codes before my arrival. " Did you tell them it costs double when they do that? :-) An e-friend of mine has factory Subie info, and tooling, and he is always saying that the SI is terrible for specifics. Broken English too. You certainly can make really good lemonade from the lemons, Mike.
Thanks Geoff, I always preach to check fuses. I let the rabbit take me down the hole with them on this one. Maybe I will learn someday. -Mike
Thank you for the Case Study! Do you know why the fuse was blown?
Hi Ray, Not sure on that one. There was no evidence of bare wires or pinched wires. The diagram only showed the fuse feeding the wireless module but it was a simplified diagram. I wonder if it feeds the power port? (lighter)
The body shop was working near the back end of the vehicle. I would connect an amp clamp at the fuse and then ck the harness where the body damage was. Put 2 to 5 seconds of time per division and set a high scope sample rate, so you don't miss any amp glitch. Even if the fuse does not blow, the short amp draw time may be too short to blow the fuse, but the amp spike might help show you where
Hi Ray, Good suggestion. In this case the damage was far from the wiring in question. I really don't think the two are connected to one another. The body shop just got hooked with the problem. I think the vehicle has been shipped by now. Thanks, Mike
I'm just seeing your post, good job! I had a similar experience last August on a 2016 Subaru Forester XT, non-push start. Interior fuse box, #15 -10 amp fuse, intermittently blowing rendering keyless entry and dome light's inop, also killed power to MFD (multifunction display) clock. This car also had right rear body shop repairs and the Keyless / TPMS module is also located in the rt. rear…