ECM Pin E21 Purpose?
02-15-2017, 01:03 AM
#1
ECM Pin E21 Purpose?
For the 3vze M/T ECU:
I have been troubleshooting codes for TPS and IAT sensors that share a common sensor ground (E2). What is the purpose of the pin (E21)? The wiring diagram says it just immediately splices into E2, so why even bother with the extra pin? My problem is that when I measure conductivity between E21 and E2, I get 2.7 K Ohms (wiring harness connector disconnected from ECU), and I should be getting no resistance since they are directly spiced (or so the diagram says).
Tomorrow Im thinking ill make a new splice for e2 and e21 at the ECU and see if the codes clear. Im confused what the point of the E21 wire is, maybe there is some reason for the resistance the schematic doesnt show? Whats the resistance measurement of your wiring harness @ E21 -->E2 ?
I have been troubleshooting codes for TPS and IAT sensors that share a common sensor ground (E2). What is the purpose of the pin (E21)? The wiring diagram says it just immediately splices into E2, so why even bother with the extra pin? My problem is that when I measure conductivity between E21 and E2, I get 2.7 K Ohms (wiring harness connector disconnected from ECU), and I should be getting no resistance since they are directly spiced (or so the diagram says).
Tomorrow Im thinking ill make a new splice for e2 and e21 at the ECU and see if the codes clear. Im confused what the point of the E21 wire is, maybe there is some reason for the resistance the schematic doesnt show? Whats the resistance measurement of your wiring harness @ E21 -->E2 ?
02-15-2017, 04:25 AM
#3
It's what's known as a "local ground" in engineering terms, there is a ground wire on each plug to keep the runs short and provide a local ground plane for filtering as soon as the signals enter the ECU.
You shouldn't have any major resistance in the splice.
You shouldn't have any major resistance in the splice.
02-15-2017, 05:32 AM
#4
Registered User
Later model 22RE trucks do not even have the E21 wire.
I have two wiring harnesses and two ECU's from '94 22RE trucks. The truck built 10/93 ('94 model year) has the E21. The other one from a '94 truck (unknown build date, I assume later on in the '94 year series) does not have the E21. Both of them use the same ECU part number.
The harness that is missing the E21 is also missing the +B1 wire on that same connector. The +B1 also looks redundant on the wiring diagram.
I have two wiring harnesses and two ECU's from '94 22RE trucks. The truck built 10/93 ('94 model year) has the E21. The other one from a '94 truck (unknown build date, I assume later on in the '94 year series) does not have the E21. Both of them use the same ECU part number.
The harness that is missing the E21 is also missing the +B1 wire on that same connector. The +B1 also looks redundant on the wiring diagram.
Last edited by rustypigeon; 02-15-2017 at 05:39 AM.
02-16-2017, 05:55 AM
#5
Based on my experience with T100's, year to year changes can end up with odd layouts at the ECU pinouts. For me I had crank and cam sensor ground wires separate pins in 97, and sliced together in 98. Measure the resistance between the two pins on the ECU to see if it's internally connected or not, if it is, then the splicing the two together wouldn't make a difference and would be a waste/extra problems down the road.
I can't see enough of the wire diagram to see if that's the common ground for the two sensors you're having problems with, but it could be possible where they splice off it has a bad connection. Personally I'd get a paper clip or something to plug into the ecu connector (might have to hammer it flat and file some) and use a multi meter to measure resistance to each sensor it splices to and see if there are any patterns. While you're at the TPS and such, you could also check the other signal wires that goes to the ECU for high resistance too. Naturally the wire will have a little resistance (generally 1-50 ohms sometimes up to 100 ohms like my body ground though steel ended up at 83 ohms on my T100), but 1k or more is more than it should be. Should be a fairly easy process as long as the sensors are fairly easy to get to. Pin 1 generally is top left pin looking at the plug. Seems most are the same style (male vs female), the opposite style of plug starts the pin out on the top right (generally sensor side).
As for your thread title, like the above poster said, it's a localized ground, it doesn't go to the body ground and is used for the sensor grounds, the sensor signal wire is the positive side basically even though most are resistance based so no true positive/negative. I like this design over the common ground design where a bad ground gives really funky effects in other electronics. Like turn the blinker on and radio lights flash or w\e.
I can't see enough of the wire diagram to see if that's the common ground for the two sensors you're having problems with, but it could be possible where they splice off it has a bad connection. Personally I'd get a paper clip or something to plug into the ecu connector (might have to hammer it flat and file some) and use a multi meter to measure resistance to each sensor it splices to and see if there are any patterns. While you're at the TPS and such, you could also check the other signal wires that goes to the ECU for high resistance too. Naturally the wire will have a little resistance (generally 1-50 ohms sometimes up to 100 ohms like my body ground though steel ended up at 83 ohms on my T100), but 1k or more is more than it should be. Should be a fairly easy process as long as the sensors are fairly easy to get to. Pin 1 generally is top left pin looking at the plug. Seems most are the same style (male vs female), the opposite style of plug starts the pin out on the top right (generally sensor side).
As for your thread title, like the above poster said, it's a localized ground, it doesn't go to the body ground and is used for the sensor grounds, the sensor signal wire is the positive side basically even though most are resistance based so no true positive/negative. I like this design over the common ground design where a bad ground gives really funky effects in other electronics. Like turn the blinker on and radio lights flash or w\e.
