Possible to fry the PCM/ECU by using multimeter to diagnose DPFE sensor?

[deezkits]

I was attempting to diagnose the DPFE sensor in order to figure out why my truck is throwing an EGR related check engine code. But I went to start the truck with back probes installed on the electrical connector coming from the PCM and it wouldn’t start. The lights on the dash turn on and shit, but the starter doesn’t want to turn over.

i do have issues occasionally with the starter not wanting to engage or needing a jump. My oil pan is leaking.. and gets the bottom ring terminal (which is the hot lead?) for the starter wet. But I made sure to clean it off and tighten it up. Nothing though. I even tried manually jumping the starter on the solenoid. And my buddy tried pop starting the truck (it’s a 5spd) and that didn’t even work.

Kind of at a loss right now, I left the truck at work yesterday Which isn’t a big deal for a couple days while I figure this out.

another note: I tried using my crappy Bluetooth OBDII reader to connect to the truck, but it wasn’t connecting..

 

[Dirtman]

What's the battery voltage.

 

[deezkits]

What's the battery voltage.

it is low, but when I’d be trying to crank it was around 11.5. That’s thing, I was messing with it trying to get it to start and kept needing to top the battery off cause the lights on the dash would keep dimming. My friend also noticed a bit fuel on/underneath (from the front) lefthand side injector rail. Not sure that’s about but don’t think it’s related to not wanting to crank over.

 

[deezkits]

What's the battery voltage.

plus, it wasn’t cranking with My jumpPack on there or jumper cables to another car or pop starting it.

 

[Dirtman]

Do a voltage drop test on the ground cable and charge/replace the battery. Push/roll starting it wont do anything if the battery is dead because the PCM still needs full voltage to operate. And using a jump pack wont do anything either if the cables from the battery are trash same for jumping the solenoid.

 

[deezkits]

Do a voltage drop test on the ground cable and charge/replace the battery. Push/roll starting it wont do anything if the battery is dead because the PCM still needs full voltage to operate. And using a jump pack wont do anything either if the cables from the battery are trash same for jumping the solenoid.

do you mean a voltage drop test to the starter motor? I see what you mean though, never considered that

 

[Dirtman]

Test battery voltage at the battery terminals and write that number down (if its under 12.2 your battery is dead anway so just stop and fix the battery), then keep the positive lead of your volt meter on the positive terminal of the battery but put the negative lead on the starter case. If the voltage is lower you have a bad ground cable.

Now do the same for the positive side, leave the negative lead of the volt meter on the battery terminal but put the positive lead on the starter lug. If the voltage is lower here, then you have a bad positive battery cable.

Worth also testing for drop to the engine compartment fuse block too since it uses a seperate positive and ground wire than the starter.

 

[deezkits]

Test battery voltage at the battery terminals and write that number down (if its under 12.2 your battery is dead anway so just stop and fix the battery), then keep the positive lead of your volt meter on the positive terminal of the battery but put the negative lead on the starter case. If the voltage is lower you have a bad ground cable.

Now do the same for the positive side, leave the negative lead of the volt meter on the battery terminal but put the positive lead on the starter lug. If the voltage is lower here, then you have a bad positive battery cable.

Worth also testing for drop to the engine compartment fuse block too since it uses a seperate positive and ground wire than the starter.

I see, I’ll give those a shot. I did come in and quickly check the voltage on the battery before I started my shift, and it looked like it was reading 6 volts. My multimeter does act funny, I put it on DCV and the numbers just fluctuate until I actually take a reading on something. I’ll be glad if i just need to change the battery although I feel like an asshat. Gonna swap out with my buddies battery and see if big yeller cranks over.

 

[deezkits]

Test battery voltage at the battery terminals and write that number down (if its under 12.2 your battery is dead anway so just stop and fix the battery), then keep the positive lead of your volt meter on the positive terminal of the battery but put the negative lead on the starter case. If the voltage is lower you have a bad ground cable.

Now do the same for the positive side, leave the negative lead of the volt meter on the battery terminal but put the positive lead on the starter lug. If the voltage is lower here, then you have a bad positive battery cable.

Worth also testing for drop to the engine compartment fuse block too since it uses a seperate positive and ground wire than the starter.

excuse my ignorance, but would the truck have to be in the key on position or be attempting to start it while measuring for voltage drop? Because of the starter relay?

I suppose it doesn’t need to be on then, I didn’t realize how the starter/solenoid worked. I’m guessing the positive cable to the starter solenoid is always hot..

Fresh battery did not start it up by the way.

 

[Dirtman]

No key does not need to be on. The large lug of the solenoid is always live.

 

[deezkits]

No key does not need to be on. The large lug of the solenoid is always live.

so I’m not seeing any drop on the starter cables.
I’m guessing this is the positive for the fusebox..? I checked that to the ground on the battery and it looks good.

I also discovered a good amount of fuel inside my airbox, this must be related to my EGR issue. The MAF sensor looked moist and the PVC tube from the bank on airbox side is wet too. No idea what’s happening LOL

 

[deezkits]

I actually discovered this just now. Tried tightening that nut and the stud just rustified itself the **** off

 

[Dirtman]

What connection is that? Hard to tell from the pic... but it obviously wasn't connected properly.

 

[deezkits]

What connection is that? Hard to tell from the pic... but it obviously wasn't connected properly.

looks like it WAS the Pos cable going from solenoid to starter :thumbs up:

 

[Dirtman]