Construction and Road Equipment
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Answered in 8 hours by:
4/22/2021
catmastertech, Technician
Category: Construction and Road Equipment
Satisfied Customers: 3,917
Experience: Field service technician for CAT 19 years.
VerifiedHey, sorry to hear you are having these problems. I know that can be frustrating. Hopefully, we can get you back to work quickly. I see no one could help you earlier, and I hope this is not too late to be helpful. Please note that I am not set up for phone calls, you can ignore the site pop-ups. We can post to this chat as much as you like to work through this issue. All experts are not employees, and we work from home in our spare time to answer questions.
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Please post only one question subject at a time. It makes it hard to respond to multiple problems in the same post.
Which unit do you wish to start troubleshooting?
Have you retrieved a fault code list?
By the way, you do have a diagnostic indicator lamp under the cab on the right side near the step.
This red LED can blink a flash code and we can use this to see what codes are logged in the ECM.
See the image below for reference.
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Information is shown on diagnostic indicator (3) by flashing the indicator ON and OFF. The information that is flashed represents a two digit number. There is a series of flashes that represent the first digit. This is followed by a one second pause. The final step is a series of flashes that represents the digit in the second position. Count the number of flashes in order to determine each digit. A pause of about three seconds separates each two digit number.
The ECM uses the diagnostic indicator in two different modes. The two modes are given below:
Normal Mode
Service Mode
When power is applied, the ECM enters normal mode. Removing the machine identification plug from harness code connector 4 places the ECM in the service mode. Once in service mode, grounding different connector contacts of the harness code connector causes the ECM to flash diagnostic codes on the indicator. This diagnostic code is a two-digit number that corresponds to the normal Caterpillar service codes.
Harness code connector 4 is located under the platform on the right side of the machine. The connector provides access to the service inputs. Connector contact 1 is grounded to flash diagnostic codes for active faults. Contact 5 is grounded to flash diagnostic codes for inactive faults. Contact 3 is used in order to clear the diagnostic codes for all inactive faults from the ECM. Connector contact 2 is ground.
Normal Mode
When voltage is applied to the ECM and the machine identification plug is installed, the ECM flashes the machine code on the diagnostic code indicator. After flashing the machine code, the ECM enters normal mode and the diagnostic indicator is turned OFF. If a diagnostic code is detected, the diagnostic code indicator remains in the ON position.
Normal Mode is used during normal machine operation. In normal mode, the ECM continuously checks for faults in the electronic control system. When a diagnostic code is detected, the diagnostic indicator is turned ON. See Service Mode.
Service Mode
The ECM detects diagnostic codes that occur in switches, sensors, solenoids and the related harness circuits. A diagnostic code is detected when the signal at the control connector is outside a valid range. The ECM records the diagnostic code.
If the diagnostic code indicator is ON and the diagnostic code indicator is in normal mode, diagnostic information is available in service mode. The service mode allows service personnel to see diagnostic codes that are detected by the ECM. The service mode allows service personnel to clear the diagnostic codes that are detected by the ECM.
To enter service mode, disconnect the machine identification plug from the harness code connector. When in service mode, the diagnostics of the ECM are available to assist with the troubleshooting of diagnostic codes that are detected. The detected diagnostic codes are shown by flashing a diagnostic code on the diagnostic code indicator. This code is a two-digit representation of normal Caterpillar service codes. The codes consist of two three digit codes (CID and FMI) that are used to specify each detected fault. Each code that is flashed corresponds to specific identifiers. The identifiers are listed below:
Component Identifier (CID) - The CID indicates the component that is faulty. The engine speed sensor or the transmission speed sensor are examples. The CID is a three digit code.
Failure Mode Identifier (FMI) - The FMI tells the type of failure that has occurred. Examples that are seen are listed: voltage above normal, current below normal and abnormal frequency. The FMI is a two-digit code.
Note: The diagnostic code that is flashed on the diagnostic indicator must be converted to a CID and to an FMI. In order to make the conversion, use the Troubleshooting, "Diagnostic Code List".
The diagnostic code for the first available active fault is shown upon entering the service mode. The diagnostic code that is shown is on hold. When a diagnostic code is on hold, the code is shown continuously. The diagnostic indicator continuously flashes the diagnostic code for this active diagnostic code. This is maintained as long as connector contacts 1 and 5 remain open.
Scrolling through the diagnostic codes shows all of the codes that are active one at a time. The connector contact for grounding 1 causes the diagnostic codes to scroll while in service mode. In order to stop the scrolling, remove ground from contact 1 when the desired diagnostic code is shown. The diagnostic code that is shown is now on hold. A diagnostic code of "11" indicates that there are no active faults.
In order to cause the diagnostic codes to scroll, ground connector contact 5. In order to stop the scrolling, remove the ground from contact 5 when the desired diagnostic code is shown. The diagnostic code that is shown is now on hold. A diagnostic code of "12" indicates that there are no diagnostic codes that are inactive.
Clearing a diagnostic code removes the diagnostic code from the memory of the ECM. When a diagnostic code is corrected, it is necessary to remove the diagnostic code from the memory of the ECM. Connector contact 3 must be grounded in order to remove a diagnostic code from the memory of the ECM when the diagnostic code for an inactive diagnostic code is on hold. After the diagnostic code is cleared, the diagnostic indicator is turned OFF. This indicates that the diagnostic code is erased. Scroll through the diagnostic codes that are active in order to remove the diagnostic code indicator from the OFF position. Scroll through the diagnostic codes that are inactive in order to remove the diagnostic code indicator from the OFF position. The ECM does not allow active diagnostic codes to be cleared.
The ECM leaves service mode when the machine identification plug is connected to the harness code connector.
Diagnostic Example
The diagnostic indicator is ON.
Diagnostic code "31" is flashed - Use Troubleshooting, "Diagnostic Code List" in order to determine the numbers of the CID and of the FMI that correspond to a code of "31".
CID 0641 - CID 0641 means that the diagnostic code is in the circuit for the forward solenoid .
FMI 05 - Failure mode identifier 05 means that there is an open in the circuit concerning CID 641.
Your hearing is better than mine. I use a screw drive to feel the end of the coil for magnetism and I can tell it is own if it sticks.
The solenoid #6 is common for both 3rd and 4th speed. I suspect is is bad as it is a little under the others.
Swap the coil with the one above it to see if it brings back 3rd and 4th.
Image below is the control valve.
Test from the ECM pin 36 to pin 39 for the circuit resistance. The wiring should have less the 5 ohms resistance. Make a jumper wire and insert it in place of the coil to test only the wires.
See image for ECM wires. SPD SOLENOID 3 OUT is to solenoid 6. CAT likes to make it confusing.
Maybe the attached image will help you see how to scroll through the codes and check the logged codes. (see below)
14 would mean no codes on a 928G
41 would mean a short to ground on the forward high solenoid.
Test Step 1. CHECK FOR A SHORT TO GROUND.
Turn the key start switch to the OFF position.
Disconnect the machine harness from the control module.
Measure the resistance from contact 2 to contact 31.
Expected Result:
The resistance is greater than 5,000 ohms.
Results:
YES - The resistance is greater than 5,000 ohms. The solenoid harness does not have a short to ground.
Repair: Connect the machine's harness. Verify that the diagnostic code is active. If the diagnostic code is present, the transmission electronic control module has failed. Replace the transmission electronic control module. Refer to Testing and Adjusting, "Electronic Control Module (ECM) - Replace".
Stop.
NO - The resistance is NOT greater than 5,000 ohms. The solenoid harness has a short to ground or the solenoid has a short to ground.
Repair: Repair the harness or replace the harness or the solenoid.
Stop.
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