Cat 277C yellow exclamation warning and beeper.

[uzz32soarer]

Hi Guys, I'm a newbie here from the other side of the World but I'm having an issue that needs some outside expertise. I have a 277C with only 200 hours on it, but it is three or four years old. Last week it started showing a yellow exclamation warning on the left side top panel. I don't have the top right panel so no way to read codes. If the yellow light was on it would steer slightly to the left in the straight ahead position and you have to keep pushing it back. Really annoying.

In desperation I purchased a CAT ET system and it has a code E568 and says left drive motor speed sensor #1: Erratic, Intermittent or Incorrect Then another one that says Left Drive Speed Sensor #1: Abnormal Frequency, Pulse Width or Period?

Any clues as to what this could be?

I've followed the wiring where it exits the lower side of the cabin and attaches to the hydraulic lines. There is a plug there and I removed and cleaned that but it was clean as can be inside. Very well sealed. There isn't any physical damage to the wiring that I can see. You can trace with your fingers and a mirror and see that the wires go into the back of a silver steel housing which is probably the speed sensor itself.

Could loose tracks make one side go faster than the other and upset the ECM? I've only recently purchased the machine and done less than 20 hrs on it but I don't think it's even had it's first service let alone had the tracks adjusted ever.

At first the light and beeper came up and stayed on until forward motion stopped and hand was off joystick. Then after a while it actually stopped the machine, no forward or backward motion just the bucket still operating fine. Turn off the machine and do a full restart and it came back again.

Back to the shed with it, checked filters, air intakes, levels etc, topped up the hydraulics which were 8 liters down and cleaned the pre air filter which was nearly clogged with fine dust and I was sure that this would fix it but the next time it went out it repeated the same fault.

Here's a picture of the screen dump created by the CAT ET.

 

[Mark250]

Hi, lift the cab and swap the speed sensor plugs over ie right side plug to left side motor and report back
DONT FORGET SERIAL NUMBER

 

[uzz32soarer]

Hi Mark250

It's a track loader machine so I'm thinking that the speed sensors are on the outside and tucked down behind the tracks at the motors. Seem to be horrible to get to.

 

[Mark250]

yes they are ,but with the 2685 and 2686 codes it does point to the sensor or the wiring to that sensor ,I do know that at the back of the motor there is a cover over the sensor and the wires fray at that point . worth a check
it is also worth while removing the sensors and check for damage or debris on the ends
I don't mean to scare you but according to SIS that error code 0568 indicates large speed differences between actual motor speed and desired motor speed cat indicates that the primary cause of this code is pump failure
do you also have an active E695
if you need help troubleshooting the sensor wiring please ask. some one will be able to help
mark

 

[uzz32soarer]

Looks like some lost time over the weekend hunting this down. Definitely no active codes and never seen an E695 come up. Thanks Mark250, I'll go hunting a bit deeper.

 

[Welder Dave]

200 hours, I think I'd call the dealer even it is a few years old and see if they'd cover it under warranty. 200 hours isn't even broken in.

 

[Nige]

Uzz, Do you have the Electrical Schematic for your 277C..? If not do you want one..?
If yes send me a PM with your email address and your machine Serial Number.

 

[uzz32soarer]

Thanks to Nige for the electrical schematic.

Today I spent hours trying to trace the issue. Cabin up, external covers behind the tracks off and then traced the wires from ECM to sensor on both sides. The right side cable was beautifully placed in a cleft created by the two hydraulic lines. Well protected and laid. Left side was a mess. Wrapped around hydraulics, more exposed, clearly no care placing that when the machine was wired. Off with the cable ties and lay the look properly and inspect every cm at the same time. Pop off both plugs and they were perfectly clean, not even a spec of dust had penetrated the plug seals.

The sheath close to the sensor was wrapped around the hydraulic fitting and then went down to the sensor but there were two small perforations in the sheath close to the large hydraulic nut. I pulled the sheathing back and couldn't see any damage to any of the four wires though.

Once I was happy with everything, I closed up the machine and tested it. I also found that the tracks were about 24mm and 28mm slack and should be 12 - 14mm with a 45kg load so I adjusted these at the same time and did a full grease job.

I barely moved the machine before I got the dreaded ! warning and the damn beeping. Instantly the machine slewed to the right and was difficult to straighten. 200m of driveway improved the handling a little but it still pulls left and even after multiple restarts the ! warning and beep don't go away.

My CAT ET interface unit comes up with the same error but this time the error is active and can't be cleared. So it appears that I may have had a dodgy wire or sensor and moving things has made it worse and now it's plating up constantly.

Bugger!!

So looking at that sensor via a telescopic mirror, I tried and tried to get a tool on the head of the retaining cap screw but to no avail. Unless there is some crazy tool it appears that either the main hydraulic feed needs to be removed or the motor slid out to allow clearance to get an allen key in there. A two minute job on a wheeled machine looks to be a nightmare on a tracked machine.

Without an SIS I'm a bit stumped as to how to replace that sensor. Impossible to think that Caterpillar would not design that sensor to be inaccessible when it's clearly a serviceable item?

Has anybody here actually done one that can give me a pointer or three?

I'll order a new one tomorrow. I'll check with Cat in Melbourne but I'm thinking that it's going to be prohibitively expensive and I may have to get one from the States. Seems that the part number is 2623764 and it looks like the attached image. Would anyone with a parts manual care to confirm the number for me please?

 

[uzz32soarer]

Image of speed sensor.

Tried three times. Sorry I cant upload the image. It's only 77kb but it wont load.

 

[uzz32soarer]

Well thanks to Nige I've managed to repair the Beast and get back to work. Thought I'd write a little info here for other guys who may be in a similar situation with a wheel speed sensor fault. Here's a few notes to take on board before going out and spending your hard earned cash on a new sensor.

Everything I looked at on my machine indicated a faulty sensor. Especially when I checked all the loom, popped and cleaned all the plugs, and then the machine failed with lights and bells on all the time.

So back to basics care of an SIS bulletin from Nige.

It was a fault in the harness. Coming from the ECM the main loom breaks down the farther it gets into the machine. The speed sensors break away from the main loom at two plugs. Then each side has a short 650mm plug to plug loom with the four wires in it. These looms exit the sides of the machine and plug to the sensors. I started out inside the machine at the entry to the first plugs from the ECM and had 8.14v on both sides of the plug. Checking the white wire to earth and the yellow as power. I opened them and gave them a shot of contact cleaner for good measure and then closed them up and went farther down the line. No power at the sensor connector on either side of the plug?

So I removed the 650mm loom and started looking at it properly. I exposed wires at the back of the plugs and ran continuity tests with zero results. So I had to strip that four wire loom down, replace the wire 30mm from each plug end. Re-sheath and refit the loom and test again. 8.14v at the sensor. Serious wiggle test stood up and voltage didn’t change.

Fired it up and error and beep still was there so backed it out and drove around the shed and did a couple of pirouettes but the error stayed. Had to clear some scrub quickly so started towards that and about 30m later the error code disappeared and never came back. Tomorrow I’ll connect it all up and code check and clear but it appears to be a happy little machine again.

It was a bit tricky. Four wire harness with no numerical markings anywhere but white / purple and two yellow wires. One with 8.14v and the other with 5.27v? Who else but Caterpillar would do that? So if you ever get this error, look first to checking that you have an 8v +/- 0.5v reading to the sensor. Then there are some other Ohm readings to check and verify before you go out and order a sensor.

In my case, who could imagine on a 200 hour machine that a wire could separate inside a protective sheath where it doesn't even rub on anything. Strange thing to hold a length of wire 600mm long and run a continuity check on it with a zero result. You look twice and just go "WTF?" to yourself.

Sure goes to show that it's useless simply replacing parts on a whim without doing the diagnosis correctly first to determine exactly what's wrong. My issue cost me a few lost hours but I was able to repair it myself with zero cost and zero parts.

Thanks again to Nige and other members here for their valuable input.

 

[Nige]

The speed sensors break away from the main loom at two plugs. Then each side has a short 650mm plug to plug loom with the four wires in it. These looms exit the sides of the machine and plug to the sensors.

That short jumper harness is shown in Grid A-12 on Sheet 1 of the actual Electrical Schematic for the machine. It's titled "MOTOR SPEED SNSR MTL JUMPER" and is an Attachment. According to the schematic the wires (white, purple, and two yellow) should all be numbered. P769 (YL), P770 (WH), 834 (YL), & 835 (PU). Maybe the numbers are hidden further up the jumper, usually they are repeated every 250mm or so in the length of every wire in a harness.

The jumper harness is readily available - indicating to me anyway that it has been in demand - maybe due to failure, who knows..? The Part Number is 258-4158 and it retails at US$51 should you ever decide it requires replacing. This compares to almost $200 for a replacement speed sensor.

In my case, who could imagine on a 200 hour machine that a wire could separate inside a protective sheath where it doesn't even rub on anything. Strange thing to hold a length of wire 600mm long and run a continuity check on it with a zero result. You look twice and just go "WTF?" to yourself.

It's known in the trade as a Cat Design Feature - designed to f**k you up .........

 

[uzz32soarer]

It's known in the trade as a Cat Design Feature - designed to f**k you up .........

Hahahahaha....................sure is!

Those wire numbers must be smaller than my old eyes can see. I looked and couldn't see anything on the wires, hence the issue with the two yellows carrying different voltages.

 

[Nige]

Four wire harness with no numerical markings anywhere but white / purple and two yellow wires. One with 8.14v and the other with 5.27v? Who else but Caterpillar would do that?

Here's what the manual says. As I suspect this is a PWM (Pulse Width Modulated) sensor. Basically it produces a square waveform signal and the width of the signal wave is directly related to the speed of whatever the sensor is measuring. The sensor produces a digital signal with a duty cycle that varies as the condition changes. The frequency of this signal is relatively constant and the frequency contains no information. Below is a graphic showing what the square wave from a PWM sensor looks like for 10%, 50%, and 90% duty cycle.



Also I cleared up another question - the sensors #1 & #2 are both in the same housing which explains why there is physically only one sensor but there is a common power feed and return, so if Diagnostic Codes come up for both sensors the logical culprit is either the power or the return.



The sensor is fed with a regulated DC voltage produced by the ECM, therefore between P769 (power) & P770 (return) the voltage should be 8.0+/-0.5V DC.
The wires 834 YL & 835 PU are for the digital sensor output signals therefore any voltage measured between either of those wires and any other wire will be meaningless.

 

[uzz32soarer]

Hi Nige, the beast has been behaving well since finding that broken wire and repairing it.

Just one issue. I'm getting an hour glass popping up next to the hour meter. It started at about 240 and now still there at 260. Not all the time but I suspect its there about 80% of the running time. I figured it might be a reminder that the 250 hour service was due but I did the service and then went in to my CAT ET to input the service data and can't find anything there that indicates a service warning code clearance.

Any idea what this could be. Just a small hour glass symbol next to the digital hour meter.

 

[Nige]

This is what the O&M Manual says and I'm buggered if I can understand it. When it refers to the Digital Display window it means the window in which the Hour Meter reading is displayed.

The left side Digital Display window displays the Service Hour Meter (SHM).

The SHM displays the hours of machine operation. This feature is also referred to as the total operating hours of the machine. Use this display in order to determine the service hour maintenance intervals.

The functions of the SHM are listed below.

The functions of the SHM in a system without a synchronized system clock:-

The following will occur when the speed of the engine is greater than 150 RPM or when the frequency at the alternator R terminal is greater than 20 Hz:

Hours will accumulate in tenth hour increments.
Hours are logged in 6 minute intervals.

The following will occur when the speed of the engine is less than 200 RPM and when the frequency at the alternator R terminal is less than 50 Hz :

The hours will retain the currently stored value.
When the maximum value is reached, the maximum value will remain in memory until a reset is performed. Cat Electronic Technician is used in order to make a reset.

The functions of the SHM in a system with a synchronized system clock follow:

The SHM will operate within the requirements of the synchronized system clock.

Note: The C model Steer Skid Loaders support the synchronized system clock.

 

[uzz32soarer]

Clear as mud isn't it Nige.

So it appears that I have a synchronized system clock whatever that is and that clock is synchronized to my Service Hour Maintenance intervals. This sort of makes sense and I suspect is why I'm getting the egg timer symbol as it came up before the 250 hr service and is still there even though I've done the service. There must be some way to tell the machine that the service has been completed but if it's in the CAT ET then I can't find it.

 

[Nige]

I know it might sound kind of counter-intuitive but have you tried asking your dealer..?

 

[DSHEQUIP]

Well thanks to Nige I've managed to repair the Beast and get back to work. Thought I'd write a little info here for other guys who may be in a similar situation with a wheel speed sensor fault. Here's a few notes to take on board before going out and spending your hard earned cash on a new sensor.

Everything I looked at on my machine indicated a faulty sensor. Especially when I checked all the loom, popped and cleaned all the plugs, and then the machine failed with lights and bells on all the time.

So back to basics care of an SIS bulletin from Nige.

It was a fault in the harness. Coming from the ECM the main loom breaks down the farther it gets into the machine. The speed sensors break away from the main loom at two plugs. Then each side has a short 650mm plug to plug loom with the four wires in it. These looms exit the sides of the machine and plug to the sensors. I started out inside the machine at the entry to the first plugs from the ECM and had 8.14v on both sides of the plug. Checking the white wire to earth and the yellow as power. I opened them and gave them a shot of contact cleaner for good measure and then closed them up and went farther down the line. No power at the sensor connector on either side of the plug?

So I removed the 650mm loom and started looking at it properly. I exposed wires at the back of the plugs and ran continuity tests with zero results. So I had to strip that four wire loom down, replace the wire 30mm from each plug end. Re-sheath and refit the loom and test again. 8.14v at the sensor. Serious wiggle test stood up and voltage didn’t change.

Fired it up and error and beep still was there so backed it out and drove around the shed and did a couple of pirouettes but the error stayed. Had to clear some scrub quickly so started towards that and about 30m later the error code disappeared and never came back. Tomorrow I’ll connect it all up and code check and clear but it appears to be a happy little machine again.

It was a bit tricky. Four wire harness with no numerical markings anywhere but white / purple and two yellow wires. One with 8.14v and the other with 5.27v? Who else but Caterpillar would do that? So if you ever get this error, look first to checking that you have an 8v +/- 0.5v reading to the sensor. Then there are some other Ohm readings to check and verify before you go out and order a sensor.

In my case, who could imagine on a 200 hour machine that a wire could separate inside a protective sheath where it doesn't even rub on anything. Strange thing to hold a length of wire 600mm long and run a continuity check on it with a zero result. You look twice and just go "WTF?" to yourself.

Sure goes to show that it's useless simply replacing parts on a whim without doing the diagnosis correctly first to determine exactly what's wrong. My issue cost me a few lost hours but I was able to repair it myself with zero cost and zero parts.

Thanks again to Nige and other members here for their valuable input.

I'm having the same problem...mine is a 289c though. JMP01627. It will start out fine but immediately slows and yellow ! and alarm comes on when moving left joystick. I lifting the cab, checked wiring, everything in this post. I have 8V to both sensors. Code 2685-8 when error comes on. After cleaning sensors and connections, went to test it. Everything worked fine, no sluggish, no alarm. As I was backing up to turn around, the alarm came on again and won't go out (just as before)...I dont understand if i have 8v to both sensors why is it still giving me an alarm. I also put two brand new sensors in it. Any ideas, Thanks.

 

[Nige]

Everything points to the signal from the speed sensor for the LH drive motor. Diagnostic Code 2685-8 will only be active if you operate the left joystick to command the LH drive motor to move. When the motor is not moving there will be no diagnostic code so that explains that part of it.

The issue with your Diagnostic Code is not the supply voltage to the sensor but the PWM signal that the sensor is sending to the ECM. FMI 08 indicates "Abnormal Frequency, Pulse Width, or Period". FMI 08 occurs when the frequency of the signal or the pulse width of the signal is not within the range that is expected by the ECM. CID 2685 is the Left Drive Motor Speed Sensor #1. I would be looking very carefully at the 834 Yellow wire that takes the PWM signal to the ECM from the #1 speed sensor. See post #13 on Page 1 for more explanation.

 

[DSHEQUIP]

I tested all the wires for continuity, all check good. Just fired it up again and tested it, it ran without the warning or alarm and then it came back on. Im also feeling a pull to the left...if the left drive motor was not turning at the same speed as the right, it could throw the code for the sensor correct? im replacing fluid in drive now.