So I've been trying to figure out why my tuner wasn't showing a few sensors (ECT, ACT, TPS) Well i found that the black wire on my TPS wouldn't ohm to ground...so i ran a wire from it to my firewall and wow...all three of those sensors now read. Does anyone know what would cause this. I think the center pin on the white 10 pin connector is the ground for those sensors (correct me if i'm wrong) and it would not ohm to ground either. Could this be a computer problem? I also couldnt dump my codes before either. I haven't tried since I ran that new ground wire though...I may be able to now. Any ideas fellas...i'm confused here...
No ground on TPS sensor (ran new ground and fixed it) more problems!!
- Thread starter mamatried
- Start date
-
Sponsors (?)
Start searching forums and doing google searches. Most likely pin 46 in your computer is fried. Common cause for this is the wrong O2 sensor wiring harness (they are different for 5sp vs auto). I had this problem and it took me two or three weeks to get it fixed. If you search the sites and use google, there are a few pics floating around of what to look for inside of your computer. You can pull it apart and find the burned ground and have it fixed. A local computer guy fixed mine for $10...saved a lot of money versus buying a new computer. Whatever you do, fix the problem before fixing the computer or you will just continue to fry it.
Mine wasn't the wrong harness, but further up the harness I had a short which caused pin 46 to burn up. Another common cause is someone using the wrong connector to try and dump the codes. The power for the underhood light looks a lot like the connector for the codes...the difference is it has 12v of power and will fry when you connect it to any thing else.
Do some research of the pin 46 and you will be amazed at what problems it will cause. Good luck with it and let us know how it goes.
Mine wasn't the wrong harness, but further up the harness I had a short which caused pin 46 to burn up. Another common cause is someone using the wrong connector to try and dump the codes. The power for the underhood light looks a lot like the connector for the codes...the difference is it has 12v of power and will fry when you connect it to any thing else.
Do some research of the pin 46 and you will be amazed at what problems it will cause. Good luck with it and let us know how it goes.
Here is my original post from when I had problems. JRichker posted a link on the second post, which helped me a lot.
http://www.stangnet.com/mustang-forums/833602-o2-harness.html
http://www.stangnet.com/mustang-forums/833602-o2-harness.html
thanks man. i'll check my computer for that when i get home its already pulled out anyways. i found a picture and it looks like it should be kinda obvious. as far as what caused it...theres a good chance when i tried to pull codes i hooked to the underhood light connector cause i couldn't get anything out of the test connector. for the O2 sensor harness the only thing i've done is extended the wires myself cause i have long tube headers. other then that i shouldn't have a problem with them they are reading ok on my tuning software. i need to see if i can dump codes now!! if i can that will be awesome. i'm gonna check those two connectors and see which has 12 volts so i know which one now to use!
Before you put ur computer back in, use a digital voltmeter and check your harness where it hooks up to your computer. Find the pin 46 wire, plug your battery back up (without computer in), and check the wire for pin 46 and see if there is any voltage to it. After my fix, I had about .005-.007 volts....which is essentially nothing. Let me know what you find!
Keep in mind that the ground for the TPS, ACT, ECT ,Map/Baro & EGR sensors is a condtioned signal ground. That means the ground passes through some small filtering circuit inside the computer. The signal conditioning helps remove some of the electrical noise that might otherwise upset the signals from the sensors.
Signal ground troubleshooting 91-93 5. ) Mustangs
The computer pin 46 signal ground is a critical component: it provides ground for the TPS, ECT, EGR position sensor and ACT. Signal ground is used in many circuits that have analog inputs to isolate the electrical noise. It is always separate from power ground, although both may have a common connection origination point. Signal ground usually has some conditioning that reduces the electrical noise to prevent false readings
The gray/red wire (pin 46) is signal ground for the computer. It provides a dedicated
ground for the EGR, Baro, ACT, ECT, & TPS sensors as well as the ground to put the
computer into self test mode. If this ground is bad, none of the sensors mentioned will work properly. That will severely affect the car's performance. You will have hard starting, low power and drivability problems. What sometimes happens is that the test connector gray/red wire gets jumpered to power which either burns up the wiring or burns the trace off the pc board inside the computer. That trace connects pins 46 to pins 40 & 60.
See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix to the computer internal signal ground.
If the ground for the TPS goes bad, the TPS output voltage increases and the idle speed goes up.
Troubleshooting signal ground problems:
Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.
1.) With the power off, measure the resistance between the computer test ground
(Gray/red wire) on the self test connector and battery ground. You should see less than
2.0 ohms.
2.) MAP circuit: Check the resistance between the gray/red wire on the MAP/BARO sensor and then the gray/red wire on the EGR and the same wire on the TPS. It should be less than 1 ohms. Higher resistance than 1 ohms indicates a problem with the 10 pin connector or the splice inside the main harness where the wire from the 10 pin connectors joins the rest of the gray/red wire. Next check the resistance between the gray/red wire and the negative battery cable. It should be less than 2.0 ohms.
3.) Engine mounted sensor circuit: Check the resistance between the gray/red wire on the TPS and battery ground. It should be less than 2.0 ohms. Higher resistance than 2.0 ohms indicates a problem with the 10 pin connector or the splice inside the main harness where the wire from the 10 pin connectors joins the rest of the gray/red wire.
Signal ground troubleshooting 91-93 5. ) Mustangs
The computer pin 46 signal ground is a critical component: it provides ground for the TPS, ECT, EGR position sensor and ACT. Signal ground is used in many circuits that have analog inputs to isolate the electrical noise. It is always separate from power ground, although both may have a common connection origination point. Signal ground usually has some conditioning that reduces the electrical noise to prevent false readings
The gray/red wire (pin 46) is signal ground for the computer. It provides a dedicated
ground for the EGR, Baro, ACT, ECT, & TPS sensors as well as the ground to put the
computer into self test mode. If this ground is bad, none of the sensors mentioned will work properly. That will severely affect the car's performance. You will have hard starting, low power and drivability problems. What sometimes happens is that the test connector gray/red wire gets jumpered to power which either burns up the wiring or burns the trace off the pc board inside the computer. That trace connects pins 46 to pins 40 & 60.
See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix to the computer internal signal ground.
If the ground for the TPS goes bad, the TPS output voltage increases and the idle speed goes up.
Troubleshooting signal ground problems:
Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.
1.) With the power off, measure the resistance between the computer test ground
(Gray/red wire) on the self test connector and battery ground. You should see less than
2.0 ohms.
2.) MAP circuit: Check the resistance between the gray/red wire on the MAP/BARO sensor and then the gray/red wire on the EGR and the same wire on the TPS. It should be less than 1 ohms. Higher resistance than 1 ohms indicates a problem with the 10 pin connector or the splice inside the main harness where the wire from the 10 pin connectors joins the rest of the gray/red wire. Next check the resistance between the gray/red wire and the negative battery cable. It should be less than 2.0 ohms.
3.) Engine mounted sensor circuit: Check the resistance between the gray/red wire on the TPS and battery ground. It should be less than 2.0 ohms. Higher resistance than 2.0 ohms indicates a problem with the 10 pin connector or the splice inside the main harness where the wire from the 10 pin connectors joins the rest of the gray/red wire.
i had this same problem with my mustang when i first got it. So i did the same thing just grounded the TPS and all the sensors started working again. But never found the reason it had no ground to start off with. But i guess my question is it sounds like the main cause is going to be a computer problem so should i just replace it.
Similar threads
