Cat 908H ECM Voltage issue

[Pete w]

Cat 908H 13,600 hours LMD01710
Unit came in with hydraulic leaks and a complaint that the alarm buzzer does not shut off. Other than that seems to be operating fine. Fixed the leaks and pulled it from the shop and it would only crawl. Does NOT have the creep control. full throttle speed does not change, forward or reverse, high or low gear.
checked the codes. had a few counts for ECM 8V power supply, parking brake sensor, hydro pressure sensor, and unexpected motor speed detection disabled. Replaced all three sensors and codes cleared except for power supply and occasionally the motor speed. checked all fuses, couple questionable ones and incorrect amperage ones. checked all power connections and relays. pulled both ecm connectors in case of corrosion. Everything looks fine, no broke, rubbed or questionable wires. Service manual says to check voltage at connector J1 at pin #44 and 45. Only getting about .7 volts. the next step is to re-flash the ECM. I dont have that flash file so that means a trip to Cat.
My question is what could of happened? Ive not heard of ECMS just taking a crap like that, But even then why is everything else operating normally? Called the tech line and you know how helpful they can be...Anyone else experience this issue? something else to try?

 

[kshansen]

Do you have access to a wiring schematic? I could send one of them if that would help.

Sorry but never even saw a 908H in person!

 

[Nige]

Did you replace the sensor you mentioned above as a result of carrying out the Troubleshooting Procedures for the Codes you had, or just because.?

If you still have Codes why not list them and I'm sure someone will post up the TS procedures for them.

 

[Pete w]

I have ET and the service manual for the unit. I have all the trouble shooting steps, my issue is that ET is saying if i dont have the correct voltage then to flash the ECM. Just seems a bit odd to me.

 

[Nige]

So you’re following the troubleshooting procedure as per ET.? Hmmmmmm. I’ve found them a bit iffy more than once, because they don’t have all the answers. Also the problem from our point of view is that we can’t see what ET is telling you to do, making it impossible to offer alternative suggestions.

What specific Diagnostic Code or Codes are you trying to chase down.? Also do you have a copy of the electrical schematic.?

 

[mg2361]

Also the problem from our point of view is that we can’t see what ET is telling you to do

Maybe post a screen shot or two of what you are seeing??

 

[Pete w]

Correct. Ill post some screen shots when i get back to the machine. But the codes im chasing is:
Active Code: 41-4 8 Volt DC supply: voltage below normal
And occasionally Active event: E695 (3) Unexpected motor speed detection disabled which im sure is causing my drive issue
Checked and followed harness'
Replaced the speed sensor at the drive motor
Checked all fuses and relays
Checked voltage at pins specified and ET said if that isnt correct then to flash the ECM. And thats been my heartburn and question all along becuase that makes no sense to me. How can you go from "Check the voltage" to "flash the ECM" in one step. It doesnt seem like a fix to me and i dont wanna take it to cat on a whim that they just need to "flash the ECM"
I considered running a jumper wire and supplying the 8 volts to see what would happen but im also afraid of frying the ECM.

 

[Nige]

Just remember that the 8v is a stabilized digital voltage produced in the ECM, not just common-or-garden 8v DC.

I would agree with you that if you have drive issues that the E695 is probably the one you need to be more concerned with. Let me see what I can dig up.

 

[Nige]

OK, so looking at the electrical schematic there are five 8v digital sensors on that machine, maybe less if you don't have creeper control. If you were missing the 8v from the ECM as a supply to those sensors then surely none of them would function correctly.?

Have you tried measuring the voltage between Pins A & B at the throttle pedal or the inching pedal sensor as confirmation.? EDIT: If there is no 8v then neither of those pedals should function correctly and let's face it they are somehwat critical to the correct operation of the machine.

IMO there ought to be a -4 Diagnostic Code for each of the 8v sensors indicating that the voltage of the sensor signal is below normal (has to be surely if there is no power being supplied to the sensor). Have you seen any of the following - 91-4, 2305-4, 2716-4.?

Back to the diagnostics of the 41-4. The 8v is produced in a sub-circuit inside the ECM. If something goes screwed in that circuit (or the instructions in the flash file software that activate it) - no 8v. If there is no 8v then flashing the ECM is the last resort to try to restore the function. Think of the ECM as a computer that has no self-repair facility. If re-flashing the software doesn't fix the problem then the ECM is toast unfortunately.

 

[Nige]

Regarding the E695, have you followed the troubleshooting flow chart in the Service Manual.?
Apparently you should have either 2775 or 2776 -2 or -8 Codes as well.

 

[Pete w]

OK, so looking at the electrical schematic there are five 8v digital sensors on that machine, maybe less if you don't have creeper control. If you were missing the 8v from the ECM as a supply to those sensors then surely none of them would function correctly.?

Thats been my head scratcher. The only thing not operating properly is the drive functions. Forward and reverse are a creep. And no i do not have creep control.

Have you tried measuring the voltage between Pins A & B at the throttle pedal or the inching pedal sensor as confirmation.? EDIT: If there is no 8v then neither of those pedals should function correctly and let's face it they are somehwat critical to the correct operation of the machine.

I have not tried this...will have to give that a shot. although as stated above everything operates.

IMO there ought to be a -4 Diagnostic Code for each of the 8v sensors indicating that the voltage of the sensor signal is below normal (has to be surely if there is no power being supplied to the sensor). Have you seen any of the following - 91-4, 2305-4, 2716-4.?

Id have to go back to look again for sure the codes. I had one for the parking brake sensor which was erratic because the rubber boot was torn and it was all but worn out.
I also had one for the output pressure sensor which turned out to be a faulty sensor as well.

 

[Nige]

Before you go any further I would strongly suggest to measure the voltage between Pins A & B at either the throttle or the inching pedal sensors, whichever is easier to get at. Ideally measure the voltage at both. Do this with the machine harness (arrowed) disconnected from the sensor but the power (master switch & key switch) must be ON. Measure the voltage on the machine harness side.