Run down of the week....
2005 Toyota Sienna, 3MZ-FE, Wheelchair Ramp conversion. From a shop I do work for that's pretty decent at diagnostics so I knew this one would be interesting!!
Lead mechanic said it acts up when it rains or going through a automatic car wash, So we know it's water related. Said it sets random DTC's.....TPS performance/correlation, Throttle Motor performance, & Internal PCM performance.
Engine will stall & not restart until allowed to dry out.
Poked around a little to see if anything obvious stood out....Wet carpet as the rear O2 sensor wiring is under the carpet, Had my helper pressure wash the vehicle while I looked for any sign of intrusion.......Pressure washed the engine while running....Top & Bottom. No stall???, No DTC's.
Decided to run it through a automatic car wash....Soon as the front of the van entered the & got the front wet, The engine stalled & would not restart.
No check engine lamp KOEO, No communication with the PCM, Had to be pulled back to the shop. Soon as we got back, Engine would start & run. Told my helper that their water must hit different than our water
Pulled it up on the drive on lift armed with a spray bottle of water & went front to back dosing everything with the engine running.
Got almost the whole underside of the van wet when I sprayed the left rear section where the tail light harness is & the engine stalled.
Key off....Unhooked the negative cable, Investigated the tail light harness & found the "Smoking Gun", One of the wires had rubbed through & burnt a good 7 inches of insulation off likely from the initial short circuit.
After that water would cause a "soft short"....Just enough to bring the PCM to it's knees. This was 100% caused by the ramp conversion from bad harness routing (These have the entire floor cut out & lowered)
Cut the burnt piece of wire out & replaced it, Wrapped the harness good with Scotch Super 33, Then double wrapped it again with Tesa 51036 anti-abrasion tape.
Go the crank it back up....Crank no start, Check Engine Lamp does light but no communication with scan tool. van had 2 extra PCM's in the floor board, One is dead just like the one installed....The other communicated & had a Immobilizer DTC which is to be expected. Starts for 1 second & dies (Classic immobilizer stuff) Key is not "chipped" so this van is not equipped with immobilizer.
**Odd because most Toyota's of this era do, Likely something with the conversion builder ordering it this way?
Waiting for the client shop to find a PCM without immobilizer or have this one reprogrammed.
Yes....I knocked the PCM out in pursuit of the issue, Just the straw that broke the camels back. The client shop is okay with it but likely a tough sell if the vehicle owner is told the truth as they will lock-in on the fact the PCM was damaged during diagnostics.