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2003 Cadillac CTS with high voltage on the 5 v reference line
Good news. The replacement ground worked and all sensors are now working and IT STARTED! Help me understand why? Could shorted wires going To the MAF have caused a bad C1. pin 26 connection on the ECM at the connector? I’m grateful to both of you for helping on this.
YIPEE. yes I recall you mentioned wire harness damage, perhaps B+ to MAF feed shorted to low reference and smoked the ground in the computer. For no start I think the CMP is needed for computer to know TDC compression from TDC exhaust phase, but not sure.
Check maf voltage pid and compare to DVOM reading at the sensor. If similar and lower than .42V engine running (code setting criteria), take 5v ref from pin 4 of maf and jump it to the signal wire, pin 5 and the maf voltage pid should change. Or lick finger and touch B+ and touch signal wire. If PID changes , then this signal wire's good all the way to computer.
if the signal wire's still low check for a short to ground or possibly an open in the signal wire. Don't forget to check and make sure ignition 1 voltage is present at pin 2 and you have 5v ref at pin 4. We don't care about IAT and we already fixed the ground.
Im getting 12 v (14 v with engine on) on MAF line 2, and 4.8 v on line 4. No voltage on the yellow line 5 (MAF sensor line) with KOEO or with engine on. I checked continuity using a turn signal light bulb and get continuity on the yellow line from the ECM connector position 56 to the MAF position 5. The bulb burns bright so the line is good. I haven't had a chance to see the PID reading on the MAF but I think I remember before that the sensor was active.
I got my scanner Autel 906BT, and the PID shows 1.5 v at idle for the MAF, and ab out 2.3 v at 2600 rpm. The mass air flow is 0.02 lb/s at idle and just goes up slightly to 0.05 at 2600 rpm. But i don't measure any volts on the yellow line (sensor line).
I unplugged the MAF sensor and the volts went to zero on the PID, It is about 1 v plugged in.
i don't measure any volts on the yellow line (sensor line).
I unplugged the MAF sensor and the volts went to zero on the PID
Any voltage on sensor wire after you unplug the MAF?
Maybe meter's not making contact or you're in the wrong wire. Pierce the wire and short signal to ground does PID read 0? Try to pull it up near 5 volts by shorting signal to 5V ref.
Check in OBD generic (maybe substitute value?)
Can you graph the PID and shake the harness about?
Any voltage on sensor wire after you unplug the MAF? { 11 mv unplugged on yellow line MAF sensor line with KOEO, I get 1 v with it plugged in } { with the engine on, the MAF sensor line volts vary from 1.5 to 1.7 volts }
Maybe meter's not making contact or you're in the wrong wire. Pierce the wire and short signal to ground does PID read 0? { PID for MAF reads 8 mv }
Try to pull it up near 5 volts by shorting signal to 5V ref. { when I do this I get 5 V on the PID and by multimeter }
Check in OBD generic (maybe substitute value?) { I was able to use the EOBD in ISO 1430 but could not graph the MAF volts }
Can you graph the PID and shake the harness about? { shaking it varies the volts on the MAF sensor line very little, a few mv }
I think you have pretty much proved the wiring integrity of the sig (yellow) wire but you do not have it's 5v ref from the ECM at pin 56 out. Your MAF sig PID is showing 5v when you jumper it so internally the 5v sig ref has gone bad. You cannot share 5v sig's. Hate to say it but I believe the ECM is bad. :ohmy:
Don't fire the parts cannon just yet. Let's see if someone else has an idea.
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
Being wrong doesn't bother me, it's being right and not understanding why that does
Can you explain about the 5 v reference when I jumped it to the sensor line? It seems the 5 v reference line at the MAF sensor (line 4?) is reading about 4.8 volts, but I guess jumping it to the sensor line I thought would lead to a PID reading of 5 volts since the MAF variable resister is bypassed...
Impedance. A digital multimeter has a higher impedance so you get a voltage reading closer to the actual but depending on its accuracy you get 4.98 to 5.1. Analog meters are low impedance so you might get a 4.8 to 4.9. Really depends on the quality of the meter. Don't get too hung up on that though.
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
Being wrong doesn't bother me, it's being right and not understanding why that does
It seems I should recheck the yellow (pin 5 on the MAF) wire continuity of the line to the ECM connector. If I use a brake light bulb with battery positive on one end of the test bulb, and connect the other end to the unplugged MAF yellow line, then it could show the line to be shorted to ground somewhere before the ECM connector. What do you think?
Yes, and tonight I verified that the MAF sensor does not short to ground. Is it possible I have a bad MAF sensor? Can you explain why you condemn the ECM when I shorted the yellow MAF sensor line (pin 5) to the 5v reference and got 5 volts on the PID? I'm just trying to understand this.
"jumping" the 5v ref voltage into the signal wire, is testing the integrity of the wiring not the functionality of the signal. The signal circuit has its own 5v that is sent from the ECM(pin 56) to the MAF(pin 5) that is PWM to ground. No voltage on the signal wire or at pin 56 even with a new sensor points me towards the ECM and a problem with pin 56.
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
Being wrong doesn't bother me, it's being right and not understanding why that does
I get 5v on MAF pin 4 and on other sensors so that would show the ECM 5 v ref is ok I think. And unplugging the MAF causes volts on MAF pin 5 to go to zero on both the PID and back probing pin 5. Do you know if the MAF signal uses 12 v reference (MAF pin 2) or 5 v (MAF pin 4).
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