Check Engine Light
#1
Registered User
Thread Starter
Check Engine Light
New alternator, brand new yellow top battery, two different PCM's, three different ignition switches, same issue. Bouncing volt meter that sets a CEL, diag code says "low voltage condition detected".
Grounds look good, must be low voltage supply to the PCM but I can't find it!
Ideas?
Grounds look good, must be low voltage supply to the PCM but I can't find it!
Ideas?
#2
Registered User
Thread Starter
I tried bypassing the PCM (with a brand new external regulator) and it did the same thing, although I did not try using a relay to bring power straight from the battery.
To me this suggests a power supply issue TO the PCM but I just can't find it.
To me this suggests a power supply issue TO the PCM but I just can't find it.
#3
Registered User
Check this, best way is to back probe with a straight pin or something. See what the PCM is seeing with the truck running.
https://www.dieseltruckresource.com/...18&postcount=4
https://www.dieseltruckresource.com/...18&postcount=4
#4
Registered User
I remember seeing a similar problem from the ignition side, low volts causing code, related to failed wire group at fuselinks, we ran a relay circuit, like your suggesting, off the battery into the regulator "ignition sense" 12v wire and from seeing 12.5 volts, went to 14, and code problem went away,
#5
Registered User
Thread Starter
I remember seeing a similar problem from the ignition side, low volts causing code, related to failed wire group at fuselinks, we ran a relay circuit, like your suggesting, off the battery into the regulator "ignition sense" 12v wire and from seeing 12.5 volts, went to 14, and code problem went away,
#6
Registered User
When you bypass the internal regulator, it thinks it is defective and gives the low voltage condition code. I chased that rabbit around the tree a few times.
There are 3 power feeds into the PCM: Pin 3 is the direct battery feed, pin 8 is the ignition switch feed, and pin 57 is the auto shutdown relay feed. And then there is the internal regulator output. Any problem with any of these will CEL.
There are 3 power feeds into the PCM: Pin 3 is the direct battery feed, pin 8 is the ignition switch feed, and pin 57 is the auto shutdown relay feed. And then there is the internal regulator output. Any problem with any of these will CEL.
#7
Registered User
Thread Starter
When you bypass the internal regulator, it thinks it is defective and gives the low voltage condition code. I chased that rabbit around the tree a few times.
There are 3 power feeds into the PCM: Pin 3 is the direct battery feed, pin 8 is the ignition switch feed, and pin 57 is the auto shutdown relay feed. And then there is the internal regulator output. Any problem with any of these will CEL.
There are 3 power feeds into the PCM: Pin 3 is the direct battery feed, pin 8 is the ignition switch feed, and pin 57 is the auto shutdown relay feed. And then there is the internal regulator output. Any problem with any of these will CEL.
Thanks for the pin rundown, that will help.
I am not bypassing the regulator at this time. I only did it as a test to see if the voltage bounce would stop. It didn't.
So, since I used bus power I can assume there is a low voltage condition to either Pin 3 or Pin 8. Will check those with the Fluke.
Thanks.
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#8
Registered User
yes, at alt, green is sbec pcm wire, controlling output, blue is from asd, ck volts on that one, add direct battery to blue to see what pcm does to volts at battery, ive seen both high and low alt output for same reason? I also know how to abandon the pcm control to external regulation, and satisfy pcm from setting code, after disconnecting it from service, vans and motorhomes used the same pcm control.
#9
Registered User
by the way, im remembering, a half of one volt changed up or down, from loss somewhere in the harness/connections, corrected the alternator output condition
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