No 5V output from ecm
Thread Starter
5th Gear
Joined: Jul 2022
Posts: 5
Likes: 0
No 5V output from ecm
I have no 5V output from my ecm to my TPS I tried swapping ecm's and no luck. before I installed the engine I replaced the BCM because I did not have a key to start the car and did have a BCM that had an ingnition with a key. There is no 5V output anywhere else on the ecm as well. I thought of just splicing onto another output.
Any ideas? Any help would be appreciated
It is a 1995 corvette with a 1994 corvette motor.
Any ideas? Any help would be appreciated
It is a 1995 corvette with a 1994 corvette motor.
Last edited by Cburlock; Jul 29, 2022 at 03:12 PM. Reason: missed something
Advanced
Joined: Apr 2022
Posts: 67
Likes: 9
After reading
One area states "5V output from my ecm to my TPS"
Then "There is no 5V output anywhere else on the ecm as well"
Need some clarification
Do you check 5vDC reference voltage at ECM or only at sensors?
Two ECM's with identical issues--way down the list of bad ECM's--
Would suggest back to basics, power/fuses and grounds to all locations--run test jumper wires if need for power (w/in line fuse) and grounds--
Time.....................
One area states "5V output from my ecm to my TPS"
Then "There is no 5V output anywhere else on the ecm as well"
Need some clarification
Do you check 5vDC reference voltage at ECM or only at sensors?
Two ECM's with identical issues--way down the list of bad ECM's--
Would suggest back to basics, power/fuses and grounds to all locations--run test jumper wires if need for power (w/in line fuse) and grounds--
Time.....................
Drifting
Joined: Jul 2004
Posts: 1,348
Likes: 289
From: MA
I agree, you have to check for 5V ref voltage at the ECM. If it has nothing and you checked fuses, etc. then one by one disconnect the following sensors until you see 5V ref return at the ECM:
TPS sensor, then MAP sensor, ABS pump module mounted behind the driver in the bin, also check the AC pressure sensor which on my '96 was located down low on the passenger side in the AC line across from my header. That AC pressure sensor has an IC in it that uses 5V ref. Mine failed (shorted) and caused the 5V ref to drop down to 1.5V !!
I actually disassembled the sensor and measured the continuity at the IC in the Kapton flex PCB. It didn't measure a short until I applied 5Volts to it.
TPS sensor, then MAP sensor, ABS pump module mounted behind the driver in the bin, also check the AC pressure sensor which on my '96 was located down low on the passenger side in the AC line across from my header. That AC pressure sensor has an IC in it that uses 5V ref. Mine failed (shorted) and caused the 5V ref to drop down to 1.5V !!
I actually disassembled the sensor and measured the continuity at the IC in the Kapton flex PCB. It didn't measure a short until I applied 5Volts to it.
Thread Starter
5th Gear
Joined: Jul 2022
Posts: 5
Likes: 0
I have been chasing this down for awhile i replaced the abs unit first thinking that was the source of the 5v for my tps however after getting all the wiring diagrams I found it come from the ecm in fact there is no 5v anywhere coming from the ecm checked all fuses grounds etc
someone said it may be the body control module causing havic
I will try disconnecting the sensors to see if the voltage returns but odd that more than one output voltage does not appear
i did check at the ecm and there is nothing
someone said it may be the body control module causing havic
I will try disconnecting the sensors to see if the voltage returns but odd that more than one output voltage does not appear
i did check at the ecm and there is nothing
Advanced
Joined: Apr 2022
Posts: 67
Likes: 9
Judging from your description
the 5vDC reference is "shorting to ground"--either a sensor problem or wiring harness issue "short to ground"
Personally, would connect the DVOM to 5vDC reference and wiggle the harness, pull, yank and tug--see if the meter jumps to 5vDC--the "old wiggle test"--
the 5vDC reference is "shorting to ground"--either a sensor problem or wiring harness issue "short to ground"
Personally, would connect the DVOM to 5vDC reference and wiggle the harness, pull, yank and tug--see if the meter jumps to 5vDC--the "old wiggle test"--
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
The ecm terminals are somewhat fragile and easily damaged when trying to probe during testing. They see easy to spead so they don't make contact. You may want to get terminals or connectors for testing. You put yards or people parting out cars may sell off connectors cheap. Car.is obd1 are you able to get flash codes or will dic display the different module codes?
Thread Starter
5th Gear
Joined: Jul 2022
Posts: 5
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Yes I can get codes this is what originally pointed me to the tps. I swapped this car from a standard to an automatic and reflashed the computer to an auto. When I road tested it it would shift from 1 to 4th very rapidly so I must shift it manually
when I swapped to an auto I added the wiring to the transmission which seems to be working fine my only issue is the 5v references
when I swapped to an auto I added the wiring to the transmission which seems to be working fine my only issue is the 5v references
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Thread Starter
5th Gear
Joined: Jul 2022
Posts: 5
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I tried replacing the computer didn’t try harness but I don’t get the 5v from multiple locations
my next thing I guess is get a new harness and computer can’t think what else it could be
guy warned me it might be body control module messing with it
my next thing I guess is get a new harness and computer can’t think what else it could be
guy warned me it might be body control module messing with it
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Your don't necessarily need a harness because you have a problem on one wire. You need a pig tail aka a terminal with a wire made to it. You need the tools to take the terminal out of the connector to swap it. Other option is find a gm technician who does side work. Corvette f body and sports car clubs are good places to find referrals
Drifting
Joined: Jul 2004
Posts: 1,348
Likes: 289
From: MA
Before I go to the trouble of replacing the whole harness I would first at least cut the 5V ref wire coming out of the ECM. Refer to the shop manual, it will show the placement and color of this wire. Cut the wire at the ECM connector and leave enough wire when you cut it so that you can splice it back together.
Then I would turn the ignition on and see if the actual ECM is putting out the 5V ref voltage at that wire at the connector.
Doing it this way isolates the ECM ref output from everything in the harness that could be causing any loads or short circuits.
The ECM alone is responsible for producing the 5V ref voltage if it is not present with everything disconnected then you must have bad ECMs.
Also are you sure the ECM is getting the correct input voltage? The 5V ref is coming off of a regulator IC inside the ECM and that IC requires the correct input voltage to produce the 5V ref voltage. It has been a while but I believe it needed constant 12 Volts and switched 12 Volts. Again check the shop manual.
Good luck!
Then I would turn the ignition on and see if the actual ECM is putting out the 5V ref voltage at that wire at the connector.
Doing it this way isolates the ECM ref output from everything in the harness that could be causing any loads or short circuits.
The ECM alone is responsible for producing the 5V ref voltage if it is not present with everything disconnected then you must have bad ECMs.
Also are you sure the ECM is getting the correct input voltage? The 5V ref is coming off of a regulator IC inside the ECM and that IC requires the correct input voltage to produce the 5V ref voltage. It has been a while but I believe it needed constant 12 Volts and switched 12 Volts. Again check the shop manual.
Good luck!