Caterpillar 268b no crank after bad fuel pump and or filter. Now power to engine start relay with switch turn. Can jumper wire at relay.

[bill fold]

of course this is the ecm located under my left foot if I am sitting in machine. The interlock ecm.

 

[Nige]

As I tested these pins it was of course with ecm pin harness unplugged.

Why did you do that.? If I had wanted you to test the power on those wires with the connector unplugged from the ECM I would have told you so.

Ok. Everting you say listed above works when checking pins at ecm harness except in the end #64 does NOT energize.

64 does NOT.

Not surprising when power on 64 comes from the ECM and you had it unplugged.........

Also, on black on number 3 I couldn't figure out exactly how to test that as ground. Jumper wire or use a multi meter in some way?

Are you using a test light to check for power.? If so bridge the test light between 124-PK and 201-BK with the key ON. You can do this with the ECM connector unplugged if you like. The test light should illuminate.

I can't believe you pulled the ECM apart without first asking was it a good idea. I have news for you - it's not, because now the seal between the two halves of the case is broken and there is every chance damp can get into it.

 

[Nige]

Update to my update. I put the pin connector back on the ecm and put test light sharp probe into the orange #64 start relay backside and when turn switch to start I go a test light light. Confirming ecm is sending power to orange wire 64. Now I must have a loss somewhere between ecm start relay.

Agreed. Next thing to check is for power at the start relay.

Wire 306-A11 GN that leaves the interlock ECM on Pin #64 changes BOTH number and colour before it gets to the start relay. It also passes through two major harness connector plugs between the ECM and the start relay.

At CONN 8 it transforms into A346-E16 BU. Check with your probe on Pin #5 of the start relay with the key turned to the START position.

 

[bill fold]

Agreed. Next thing to check is for power at the start relay.

Wire 306-A11 GN that leaves the interlock ECM on Pin #64 changes BOTH number and colour before it gets to the start relay. It also passes through two major harness connector plugs between the ECM and the start relay.

At CONN 8 it transforms into A346-E16 BU. Check with your probe on Pin #5 of the start relay with the key turned to the START position.

View attachment 326165

Ok. I had to abandon this skid steer repair and leave machine in my shop while using other machines.
Here is what I've done since the last message.


I neatly black silicone sealed up the computer.
Put back on machine.

I replaced ignition switch after tracing all wires to and from.

I replaced parking brake switch while I had the insane upper left dash panel apart. And traced wires.

Replace the parking brake solenoid and the aluminum block it resides in.
(The o-ring of solenoid had a slight drip). But I never had parking brake issues to begin with.

Parking brake clicks and goes in and out and properly turns off on dash panel (light).

I replaced the pilot joystick main solenoid.

I have unplugged and plugged back in - the trigger and thumb wheel wiring plugs on worktool joystick to see how interlock ecu reacts.
No difference.

Cleaned out fuse panel boxes with compressed air.

Both side of all fuses work and show power.

Replaced lap bar/arm bar switch (as it was still the original). Just like before, the dash indicator turns on or off when arm bar is up or down as normal.

I cleaned all grounds except the one from the bell housing to frame (was gonna do that next). It is gonna be hard to get to!!

Replaced many, but not all relays.

Replaced relay under work tool joystick side in harness. Just because I was nearby working on it.

Replaced and swapped around relays in the upper rear above engine area (the left side). And tested all relays with a tester.

Replaced relay going to fuel primer pump.
Replaced fuel primer pump.
Replaced the backflow diode type thing on fuel pump(forgot name).

Fuel pump comes on with ignition switch turned to start...not ON. I once thought this was wrong but have now learned (correct me if I am wrong) that the fuel primer pump comes on in the START signal to start relay and "Latches on" to the start and run power and the back flow diode thing (forgot name) prevents back flow of electricity.

I bought a metal Lisle depin tool. It is the Deutsch Terminal Tool number: 59600

I know...I've heard plastic is better and doesn't damage but the plastic depin tool also breaks often. I was careful.

I carefully depinned the #64 green female pin from the interlock ecu.

Then I put a test light in the #64 hole (while harness plug is connected to ecm) to eliminate the possibility that the wire to start relay had resistance and was messing up the ecu from sending start signal power. Unless I don't have the test light hitting the little pin thing in the hole of ecm connector I'm still getting a "No start trigger output". (I will retry tomorrow to make sure there is no output from ecm to start relay)

Ok, then I took a wire, put it on the positive post it battery, ran it up around machine and clipped the end to the the green wire that I depinned from #64 and put juice to the start wire that comes from the ecu (but now depinned or unhooked). to the start relay. Then I went back to the starter relay female (left relay unplugged) where the start wire comes to the start relay and checked the voltage. My power probe digital meter shows a pure "13.0 volts". Basically, to clarify, I ran a 12 volt power through the unhooked wire from ecm start trigger and tested the voltage in the receiving end at the start relay female plug and had a pure 13.0 volts. Seems to me I have no short or short to ground in the start trigger wire to start trigger relay coming from ecm.

Keep in mind, I can jumper wire this machine at start relay and it runs and moves. I haven't gone off and taken it for a spin on the job site, but the parking brake released, the boom went up and down and when I backed it further into my shop.

The battery light is still on on my machine dash. ??????

Can this mean that the interlock ecu just randomly is shorting to ground? (Hence gone bad?

I have also replaced the alternator.
Taken off starter and had it professionally tested. I have also bypassed starter to make sure starter isn't grounding out.

Maybe I haven't ran the machine long enough to clear battery light?
The battery light may be showing on...but as I check for short to grounds in this thing I'm not finding any.

Ok, so I have also checked the door shut switch and also inserted the door off plug so that the door open or closed does not matter.

I have checked the seat switch. To make it easier to work on and test, I have crimp solder butt connected the seat switch wiring for now. Sorry OSHA.

Ok.
So, to not make this message any longer --- as it's too much to take in...I will save the "what i checked at ecm pin OHMS" list for another upcoming message. I'd like to walk through those one more time with qualified instruction to double check and be clear.

Thanks and sorry for the delay, and return with such a long message. I appreciate all help.

Not getting a start signal from interlock ECM was my original issue.

Thanks

 

[HarleyHappy]

Wow! Like a squirrel, you have been all over, looking for that nut, but, you changed so much stuff, how can you be sure you didn’t create another problem?
Basically, if an electrical component is working, replacing with a new ( cheaply made foreign part) may not be the best idea.
Still sounds like your ECM.

 

[bill fold]

Wow! Like a squirrel, you have been all over, looking for that nut, but, you changed so much stuff, how can you be sure you didn’t create another problem?
Basically, if an electrical component is working, replacing with a new ( cheaply made foreign part) may not be the best idea.
Still sounds like your ECM.

Yes. Like a squirrel chasing a nut.

I was thinking I was better off replacing a few things to eliminate them instead of paying random mechanics in my area to charge me to do the same. I kept old parts as backup. Of course I know there are qualified mechanics near the city that could probably get closer to the diagnosis without throwing parts at it.
I haven't been able to get a mechanic to drive 100 miles to come look at this thing. Only, "bring to us the dealer".

The dealer says they typically remove my interlock ecu and put in another similar machine and see if it will crank it. I can't get anyone to let me try this. They are afraid my ecu will fry their machine.


I have purchased Cat brand parts. I only replaced the parking brake switch because I had the dash torn apart and the switch was getting a little worn. Also, the key switch to freshen it up a little.



I went through a lot of tests in the ecm interlock connector pins coming from door, seat, arm bar. Worktool solenoid. Parking brake. Etc. so many that I want to start all over. As I don't have CAT SIS subscription I've had to use the "just answer" and search function on this site. It becomes so convoluted I want to restart the process of elimination with expert advice in the proper steps.

I'm being careful as Cat wants $6100 for the interlock ecu and $6100 for the hydraulic ecu.

I had no water in floorboard. Just leaves and oil and a little mud around bell housing area.

When this problem began, after the constant, the first problem I noticed was:
-main positive wire from battery that goes directly to starter had the crimp/solder on lug barely hanging by a thread. Snapped off at my touch to remove bolt from starter positive post. It looked like it had wiggled back and forth under tension or a sliding back and forth of battery under clampdown holder.

Worried that main positive wire resistance has damaged interlock ecu.

It is amazing caterpillar can't read codes or test the interlock ecu but they can the hydraulic ecu.

The $6100 price makes one tempted to try the Chinese eBay option for $900-$1500.

A company out in North Carolina has developed a test jig that simulates all of the sensors for the interlock ecu. They want $750 to test my ecu as of June 2025. Once they haven't ecu as hostage, if my unit is repairable they want $1750 to repair it. I assume the $750 comes off of the $1750.

I am assuming there is no specific cat dealer needed programming for the interlock ecu. Only the hydraulic ecu?

Thanks

 

[HarleyHappy]

I know this may sound crappy but this is where I would search high and low for a rental machine that would have that particular ECU.
I have done it on bikes before, especially when they got rid of fuses and went to BCM’s.

 

[mike holcomb]

We had a 287c i think it was, and it would blow a fuse when we'd get a heavy rain and it wouldn't crank and it wouldn't run the fuel pump. I can't remember exactly what the cause was but for some reason I think the fuel cut off selonid was going bad and that's what was causing it to blow the fuse. But again that was on a C model. Fuse panel was buy your elbow when sitting in machine

 

[Nige]

I'm being careful as Cat wants $6100 for the interlock ecu and $6100 for the hydraulic ecu.

FYI both units are available aftermarket from trusted suppliers (certainly at least one that I can speak of) at around $1200.

 

[bill fold]

FYI both units are available aftermarket from trusted suppliers (certainly at least one that I can speak of) at around $1200.

Oh good. I would love to know of the trusted supplier. I really appreciate it.

 

[bill fold]

I know this may sound crappy but this is where I would search high and low for a rental machine that would have that particular ECU.
I have done it on bikes before, especially when they got rid of fuses and went to BCM’s.

Hmmm....that is a good idea!!! Now I have to find a rental B series. Searching.,,,

 

[bill fold]

Well, I ran a hot wire to the "depinned" green wire from the start output of the ecm. It cranks and runs and operates boom up and bucket as well as travel.
I hit full throttle with engine and it had a miss and splutter.
It was then that I realized the electric fuel pump did not have a start circuit of power to latch on to. So....I turned machine off.
I turned ignition switch to "start" and I hear fuel priming pump run.
Then, I hit power to my power probe (my hot wire) that it touching the green (start signsl( output wire (that is depinned from the Ecm) and cranked it. I hit full throttle and it does NOT cut out. Runs flawlessly at full rpm.
Backtracking to the original problem...this is why I kept thinking I needed to change fuel filters the final moment I was operating it and parked it before this fiasco.

So, what does this tell me? I do not know!!??

Also, the battery light goes away when it is cranked and running. When the switch is turned to "on" and it is not cranked, the battery light is on. Maybe this is normal?

Parking brake works good. But, it seems the switch installed requires a flip to on and on and again turns it off and a flip on and again turns it on. It has no spring action. Maybe this is normal and my original switch was worn out.

I supposed I am going to have to run myself a hot wire with an online fuse (or what size) up to a momentary momentary push button switch to bypass the start portion of the interlock ecm. Ugggg...jerry rigged.

 

[Nige]

You may find some useful information, especially in the form of troubleshooting documents, in the thread I’ve linked below.

CAT 226B Parking Brake Indicator and Armrest Indicator Are Flashing

Hello, I'm trouble shooting Parking Brake Indicator and Armrest Indicator Are Flashing on my CAT 226B serial number MJH08353. In the attached picture, in purple I highlight what I believe is the detent coil. I have two questions, first, is this the detent coil? It's located under my right hand...

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