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06 envoy with 4.2 engine. Has an intermittent no crank. Noticed that when you bang on the fuse box it comes back to life. Already replaced crank relay but still does it. I noticed the ground Signal at the relay is missing with the no crank condition is there but I do have the crank power supply voltage from the ignition switch.on the crank fuse 17 I wanted to test at the ECM to see if it was a computer problem or Fusebox problem but the diagram throws me off a little bit seems to be a simple circuit but never have had training on this besides scannerdanner Premium videos. Other thing I noticed is that you have to really turn key over hard to get voltage at crank sensor 17. Simple turn the key normally will do it. Don't know where to start. Frustrated because it's in intermittent
I noticed the ground Signal at the relay is missing with the no crank condition
Ok where did you measure that ground. At the relay or PCM? Just think about it if the PCM receives no input it won't ground the control side of the relay.
on the crank fuse 17 I wanted to test at the ECM to see if it was a computer problem or Fusebox problem but the diagram throws me off a little bit
Where does it throw you off Chris.
Other thing I noticed is that you have to really turn key over hard to get voltage at crank sensor 17.
So you mean between ignition switch and crank fuse 17?
I had my son turn the key while I was checking the signal at the relay but nothing was there till after you hit it lol. The part that troubles me on the diagram is The yellow black wire from the ECM to the starter relay is supposed to ground the circuit But I back probed the yellow black wire on connector 1 pin 48 of the ECM to check my signal there and nothing as well. After I hit it pin 48 goes to ground all the time with key on then it starts fine. I was under the impression that pin 48 was only supposed to ground when ignition was on start position. I think I'm looking at it wrong
It looks like that pin 48 is only grounded while in start position or it will be cranking all the time. To check if it is a good ground you need to load a circuit with something like 5 watt bulb. Looks like there is an input problem from the Park-neutral switch which wiring goes through a fuse block (where you hit sometimes))). I would check if you are losing battery voltage on Dark Green wire 54 while in no crank situation.
Been here before on a very similar Envoy, ended up finding poorly crimped fuse box terminals. Just like yours, I could wiggle the box and make the problem come and go.
If possible, the next time it happens, try wiggling just the crank relay, see if the problem goes away.
Tyler wrote: Been here before on a very similar Envoy, ended up finding poorly crimped fuse box terminals. Just like yours, I could wiggle the box and make the problem come and go.
If possible, the next time it happens, try wiggling just the crank relay, see if the problem goes away.
Must be a common fault on these, I've seen one and a good friend of mine who works at another shop shared a similar experience with me recently.
Noah wrote: Must be a common fault on these, I've seen one and a good friend of mine who works at another shop shared a similar experience with me recently.
Yep, common feature of these trucks, unfortunately Here's hoping Chris doesn't have to replace the fuse box.
Im tired of seeing this envoy around the shop. Im trying to make it not start but starts every time. Ive explained to the owner that I need to catch it on the spot to diagnose it and feel bad throwing parts at it. Last time he took it home called me hours after with same problem. He says he bangs on the fuse box and it starts. I would hate to put a box on it and problem still be there.
chris.arriazola wrote: Im tired of seeing this envoy around the shop. Im trying to make it not start but starts every time. Ive explained to the owner that I need to catch it on the spot to diagnose it and feel bad throwing parts at it. Last time he took it home called me hours after with same problem. He says he bangs on the fuse box and it starts. I would hate to put a box on it and problem still be there.
Intermittents are the worst If you have a relay of the same type that you could sacrifice, you could test for spread pins at the fuse box. You could also use this to load the box with a small bulb and check for voltage drop. My experience says you'll find a problem at the relay pin itself, and not at the bulk connectors going into the fuse box.
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Here's hoping Chris doesn't have to replace the fuse box.