P.O.S.T. -> DT466E - stuck/stalled

[ewo1]

This post is for the those who "think" their electrical connections are just fine.... and still can't figure out on why it is not working!​

I'll explain...

I had disconnected the batteries on my bus for the winter and yesterday I topped off the charge so that they would be at max power, connected my batteries and went to turn the key switch and then it happened!

For those who do not know what P.O.S.T. means, it means POWER ON SELF TEST. all computers undergo a POST when starting up. some are visible and others are not.

On a Skoolie, it is visible. When you turn the key ON, the gauges will sweep back and forth and your dash "Idiot" lights will turn ON then turn OFF.

Well my gauges DID sweep and the "Idiot lights turned ON but would not turn OFF!

I turned the key further to START and nothing, but, the solenoid under the drivers window did click with no engine spin!
I have an Allison 3000 and the key pad, with the switch to ON, did change gears no problem, just NO CRANK!

Luckily for me electrical gremlins excites me, makes me think....so what could be wrong I asked...ECM took a dump???

As I try to tell ALL who I help, go back to square one and check your connections, power AND ground, and not just visibly check but open then back up, clean them and try again.

So I followed my own advice and want to share how important this really is, especially when chasing down a gremlin.

I have 2 batteries wired in parallel along with 2 HOT wires for the A/c units and ONE hot wire for the wheel chair lift and the ONE hot wire going to the starter.

So when I initially connected the batteries everything "Looked" clean. Not really shiny metal but clean, no corrosions or "gray" surface matter.

I had wired the ECM wires to one battery and the TCM to the other. The ECM lug was sandwiched between the two A/c hot wires thinking that it would be good enough to work. It didn't work well!

SO, I followed my own advice, undid all the battery connections, got a small steel brush and cleaned them all shiny clean, battery terminals too!

This time I sandwiched both the ECM and TCM between the battery terminal and the main (thicker) hot wires with the A/c hot wires on top of it all, then tightened securely.

Turned the key and VOILA, ECU performed it POST test completely and bus started!


What's the lesson here?
How many times have we all seen this similar issue, intermittent electrical failures causing drivability or starting issues?

The naked eye test is not enough!!!
Always go back to square one and CLEAN your contacts even if they look good to the eye!

Current flows best in a wire when there is NO or limited opposition to electron flow. Even slightly dirty connections that Look good can "oppose" or "limit" current flow where you will have a situation in which the device will turn ON but act like a drunken sailor and simply make you think you have an electrical gremlin!

I have mentioned this before, it is called a "High Resistive Open" nobody talks about this nor does anyone ever consider/talk about loading your wires with "Full" current capacity. Most just rely on a simple Ohmmeter continuity test.

An Ohmmeter test pushes minimal current down the wire. remember you are working with a small 9 volt battery that already is using its power to turn the meter ON.

This is what happened in my case. A High Resistive Open caused by dirty contacts, restricting full current flow to the ECU which in turn could not complete the POST test.

So for anyone who is chasing an electrical gremlin, always go back to square one and when in doubt, perform a load test on your wire!​