Troubleshooting for CAT dump trucks failing to shift gears automatically

The transmission system of the CAT769C dump truck is equipped with an ICM (Individual Adjustable Clutch) type transmission with an electronic power shift control system. It uses a speed sensor to input signals into the transmission control device. The device determines the shift time based on the signals and then transmits the signals to the upshift and downshift change valves. The change valves send pressure oil to the rotary brake that can rotate the selector's rotary valve to control the oil supply and discharge time of the transmission hydraulic control device, complete the engagement of the clutch, and achieve automatic gear shifting.

Due to the aging of the equipment, the fault of inability to shift gears automatically often occurs. When troubleshooting, first check whether the oil level in the transmission oil tank and the hydraulic oil tank is sufficient, then check whether the rubber hoses and connection points are leaking, whether the battery voltage is sufficient (24V), and whether the electrical connectors are loose. If all the above are normal, the fault is very likely to lie in the electrical system. The troubleshooting steps are as follows:

(1) Place the transmission selection valve and the transmission gear lever in neutral position, connect the circuit breaker and the key start switch to connect the circuit, do not start the engine, place the lift control lever in the "lift" position, and check whether all the indicator lights (light-emitting diodes) on the transmission control device monitoring panel are on. If none of them light up, the reasons are: the key start switch is damaged; The 202-YL wire from socket 2 of the transmission control device wiring harness (plug) to the ground of the body is disconnected, or the 308-YL wire from socket 1 to the key start switch is disconnected or grounded. The 105-BR wire from the key start switch to the main circuit breaker is grounded and short-circuited. The transmission control device is damaged. The monitoring panel is damaged. If the gearshift lever switch and the transmission switch indicator lights 1 to 5 are all on, but the rest of the indicator lights are not on, it indicates that the transmission control device is damaged. If the indicator lights 1 to 5 of the gearshift lever switch and the transmission switch are not all on, the reasons are: the wires in the wiring harness from the bucket lift switch to the transmission control device are damaged (open circuit). The 202-BK wire from the bucket lifting switch to the body is disconnected. The 707-PU wire from the bucket lift switch to the wiring connector of the transmission control device is disconnected. The truck bed lifting switch is damaged.

(2) If all the indicator lights are on, it is a normal display. You can place the lift control lever in the "floating" position to check whether the indicator lights (light-emitting diodes) on the transmission control device monitoring panel can display normally (the lift lever on the monitoring panel lights up normally when it is in the "floating" position). If none of them light up, the reasons are: improper adjustment of the truck bed lifting switch or damage to the lifting switch. The 707-PU wire from the wiring harness jack 7 of the transmission control device to the bucket lift switch is open-circuited. The wire 202-BK from the lifting switch of the vehicle body to the grounding of the machine body is open-circuited. The control device of the transmission is damaged. If the indicator lights of the gearshift lever switch and the transmission switch do not display normally, the reasons are: the wiring harness from the 14-pin connector head (on the gearshift lever switch socket) to the 37-pin connector plug (on the transmission control device) is damaged (open circuit). The wiring harness from the 10-pin connector socket (shift lever switch) to the 14-pin connector is damaged (open circuit). The gearshift lever switch is damaged or the transmission switch is damaged. The transmission control device is damaged. The wiring harness on the transmission switch to the oil circuit pedal assembly is damaged. The wiring harness from the 20-pin connector socket (on the driver's side) to the oil circuit pedal assembly is damaged. The wiring harness from the 20-pin connector socket to the 37-pin connector plug is grounded (short-circuited). The wiring harness from the 20-pin connector socket to the 10-pin connector plug is grounded (short-circuited). The flexible coupling is damaged. The installation (timing) of the gearshift lever switch is incorrect. If the indicator light of the gear shift coil that must be turned off is on, the reasons are: the gear shift control device is damaged; There is a short circuit between the coil and the power line. If the indicator lights of the upshift and downshift coils flash alternately, the reasons are: coil leakage; The grounding wire 202-BK in the chassis or cab wiring harness is loose (open circuit). The transmission control device is damaged.

(3) If the indicator light of the deceleration brake that must be turned off is on (under the condition that the brake is not engaged), the reasons are: the wire 706-BR in the cab wiring harness is grounded (short-circuited); The 720-PU wire in the cab wiring harness is grounded (short-circuited). The parking brake switch, deceleration brake switch and emergency brake switch are damaged. The control device of the transmission is damaged.

(4) Move the gearshift lever of the transmission to reverse and first gear up to seventh gear respectively. After each movement, check whether the indicator light of the gear device is consistent with the normal display and whether you can hear a "clicking" sound from the transmission coil. If it does not display normally and there is no "clicking" sound, the reasons are: the wire leading to the coil is damaged or grounded; Coil damage; The transmission control device is damaged.

(5) Place a tanner wrench on the shaft of the transmission selector and check if it can be manually shifted. If it can be manually shifted, the reason why it cannot be automatically shifted is that the wires 710-GN, 709-OR, and 202-BK from the socket 10 of the 20-pin connector to the speed sensor are short-circuited or open-circuited. The speed sensor is damaged. The transmission control device is damaged.

If the above inspection still fails to identify the cause of the electrical system failure, the cause of the failure may lie in the hydraulic system. In any system, the failure is likely to be intermittent (not fixed). At this time, attention should be paid to observing the diagnostic light (light-emitting diode) to determine the system where the failure occurred.