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1990 k5 Code 15 and 21 coming up

Justin Fleming

Justin Fleming

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Could this be related and are there processes to testing them?

I thought there is a voltage check on the throttle position sensor that you could check but I cant seem to locate that article

On the coolant sensor I am not sure how to check that signal
 
Justin Fleming said:
If I am testing the TPS correctly looks like it is stuck on 5 volts....
Click to expand...

one wire is 5v. one wire is ground. one wire is variable voltage based on throttle position - varies from about 0.5v to 4.5v from idle to WOT.

CTS voltage varies based on temp. you can probably search and find a chart or look in the drivability and emissions manual to find it.
 
So I am get the 5 volts on both wires, I assume the sensor is bad. If I unplug the sensor the grey wire is not at the 5v....soon as you plug it in it goes right to 5v.
 
could be. I think those two sensors may share a ground. but it's been a while since I've looked at the wiring diagrams....

but the TPS seems to be bad based on having 5v on two wires. I'd start there.
 
Anyone know where the ground wire is coming from for the TPS circuit. This appears to be the issue, intermittent ground. I put a jumper in to the ground on the battery and truck start up and works fine.
 
Justin Fleming said:
Anyone know where the ground wire is coming from for the TPS circuit. This appears to be the issue, intermittent ground. I put a jumper in to the ground on the battery and truck start up and works fine.
Click to expand...
the TPS and CTS share a ground back to the ECM, there is a splice in the harness. I think the ECM system has grounds on the front of the block by the thermostat housing and on the back of the block on the passenger side.
 
I unwrapped the wiring harness, looks like the black ground wire goes from TPS directly to the CTS. I don't see any other splice etc. Does it get its ground from the CTS itself? I can ring the wire out from the tps to the cts and it has a solid ring of continuity, I check it to ground and it has nothing....
 
Justin Fleming said:
I unwrapped the wiring harness, looks like the black ground wire goes from TPS directly to the CTS. I don't see any other splice etc. Does it get its ground from the CTS itself? I can ring the wire out from the tps to the cts and it has a solid ring of continuity, I check it to ground and it has nothing....
Click to expand...
I was also getting a coolant sensor error code, so I wonder if that has failed?
 
the TPS and CTS grounds should splice together and go back to the ECM to get ground through the system grounds. you probably need to check the drivability and emissions manual and look at the ECM pin outs in chapter 3. check continuity on the common ground wire back to the ECM.

the above only works if somebody hasn't hacked up the harness...so if you don't have the TPS and CTS sharing a common ground back to the ECM, you have your work cut out for you to put it back.
 
does the cts have teflon tape wrapped around it ?? IIRC it grounds through the threads, to the intake.
 
The only factory splice I find is the grey wires, But the black is just looping from TPS to CTS

Should I have ground on one of the pins on the CTS? I know the outter shell (hex Nut part) is good to ground...
 
that blk wire should also connect the map sensor and be spliced back to ecm cavity D2
 
So I have found the splice for the ground wire now. It appears to be fine and intact. What I have proven is for what ever reason I keep loosing the ground to the CTS and TPS intermittently, which would mean the computer is likely loosing it as well.
 
I think the ECM system has grounds on the front of the block by the thermostat housing and on the back of the block on the passenger side.

on my 1990, at the ECM, D1 and D12 are the system grounds and the TPS and CTS grounds go to A11.
 
Do these wires eventually go to the big wiring block on the fire wall or do they take a different route through the fire wall? Almost impossible to track that wire once it gets behind the distributor
 
Justin Fleming said:
Do these wires eventually go to the big wiring block on the fire wall or do they take a different route through the fire wall? Almost impossible to track that wire once it gets behind the distributor
Click to expand...
should go through the firewall on the passenger side and to the ECM behind the glove box.
 
"I think the ECM system has grounds on the front of the block by the thermostat housing and on the back of the block on the passenger side"

so these grounds would be like the master ground for the ECM? Does the ECM housing have a ground to the metal case? It appears that my ground at the thermostat housing is good, I would almost rather extend that to the battery.....

still trying to locate the ground on the passenger side back engine block....
 
engine block ground braided wire is good and good ground, going to go drop the ECM down see what I can figure out there.
 
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