Immobilizer preventing start only when cold

[winestonecowboy]

My truck has developed an interesting new issue: when it's below freezing, I get a crank no start every time. Conveniently I've only experienced this when out in the bush camping, as it has been above freezing in town for a couple of months.

When I wake up in the morning and go to start the truck, it will crank forever but not turnover. After repeated tries however, it finally cranks strong. Checked the battery, and charge is healthy, so I began to think this is a fuel pressure issue. However, the last time this happened I discovered that the key safety light (immobilizer) did not turn off when the key was inserted in these temperatures. Also, when it does crank, if I turn it off and try again, the key safety light turns off when the key is inserted and the truck starts

Do I need to go for the full immobilizer fix with this or does anybody have any ideas for easier fixes?

Edit to add that when key is inserted in freezing conditions and turned to ACC - all electronics light up and function normally.

 

[JimSoCal]

Do you have a spare key to test with? Need to figure out if it's the key, or the immobiliser.

EDIT: something to also check: My immobilizer fix - https://forum.ih8mud.com/threads/my-immobilizer-fix.946305/

 

[winestonecowboy]

Do you have a spare key to test with? Need to figure out if it's the key, or the immobiliser.

EDIT: something to also check: My immobilizer fix - https://forum.ih8mud.com/threads/my-immobilizer-fix.946305/

I don't have a spare FOB - just the one. Assuming it's the immobilizer as once it warms up it works fine.

 

[Trunk Monkey]

If it is the immobilizer issue with the EFI fuse, that's not a difficult fix, there's nothing "easier" really. There's more testing you can do in that thread linked to narrow down the issue.

 

[JimSoCal]

I would highly recommend getting another master key made. If you lose your only master key, you’ll have to remove the immobilizer and re-solder a new chip.

 

[medtro]

When I wake up in the morning and go to start the truck, it will crank forever but not turnover. After repeated tries however, it finally cranks strong.

What made it crank strong after repeated tries? Why was it not cranking strong at the beginning?

 

[winestonecowboy]

What made it crank strong after repeated tries? Why was it not cranking strong at the beginning?

That is precisely the question I’m wondering. I feel like it’s something to do with the electronics warming up?

 

[medtro]

That is precisely the question I’m wondering. I feel like it’s something to do with the electronics warming up?

How long did it crank before it became cranking strong? Do you think electronics can warm up to cause a difference in that amount of time? I am guessing loose connection. Vibration from cranking may have helped with the loose connection.

 

[winestonecowboy]

How long did it crank before it became cranking strong? Do you think electronics can warm up to cause a difference in that amount of time? I am guessing loose connection. Vibration from cranking may have helped with the loose connection.

It will take a while, depending on how cold it is. Typically it's a few minutes of repeated tries. I'm 99% positive it is a temperature thing. I drive the truck 7 days a week and it starts up fine and with the same cadence each day. If it was a loose connection I would probably experience it semi-regularly, right?

Only when out at higher elevations when the temp is below freezing does the immobilizer do this. I think there is something very subtle going on somewhere

 

[medtro]

If it was a loose connection I would probably experience it semi-regularly, right?

I was thinking loose connection when cold. Metal shrinks when cold, may be if shrinks enough to cause loose connection.

 

[winestonecowboy]

I was thinking loose connection when cold. Metal shrinks when cold, may be if shrinks enough to cause loose connection.

Ah. That tracks. Likely buried in the fusebox I'm assuming