621H, 623H and 627H Wheel Tractor-Scrapers Power Train Caterpillar

Before you begin the troubleshooting, refer to Systems Operation, Testing and Adjusting, "Machine Preparation for Troubleshooting".

Note: For additional information, refer to Systems Operation, Troubleshooting, Testing and Adjusting, "Transmission/Chassis Electronic Control System" for your machine.

The transmission does not shift to all speed positions.

Probable Cause

• Foreign material or a damaged component does not permit movement of the ECPC valves.

The ECPC solenoids do not activate.

Probable Cause

• The ECPC solenoid is broken or damaged.

• The ground wires are not connected properly.

• The electrical wiring to the downshift solenoid is broken or damaged.

• The harness to the ECPC solenoid is broken or damaged.

The machine turns when the differential lock is engaged.

Probable Cause

• The differential lock switch is worn or damaged.

• The differential lock solenoid is worn or damaged.

• There is no pressurized oil at the differential lock solenoid, the quick-release valve, or the differential lock cylinder.

• The quick-release valve is worn or damaged.

• The differential lock cylinder is worn or damaged.

• There is an electrical malfunction with the differential lock system.

The machine cannot make a complete left turn or a complete right turn after the differential lock is released.

Probable Cause

• The differential lock switch is worn or damaged.

• The differential lock solenoid is worn or damaged.

• There is pressurized oil at the differential lock solenoid, the quick-release valve, or the differential lock cylinder.

• The quick-release valve is worn or damaged.

• The differential lock cylinder is worn or damaged.

• There is an electrical malfunction with the differential lock system.

• Worn or failed inner clutch jaw retention bolts.

The machine does not automatically upshift at the correct rpm.

Probable Cause

• The output speed sensor for the engine is broken or damaged.

• The hydraulic system is worn or damaged.

• The affected ECPC valves are not working properly.

• The electrical system is not working properly.

The transmission does not operate in REVERSE, FIRST, or SECOND speed but the transmission operates in THIRD through EIGHTH speeds.

Probable Cause

• No. 1 clutch is not engaged because of low oil pressure.

• No. 1 clutch is not engaged because of discs and plates that have too much wear.

• No. 1 clutch is not engaged because of broken components.

• malfunction of the transmission control.

The transmission does not operate in REVERSE speed but the transmission operates in FIRST through EIGHTH speeds.

Probable Cause

• No. 7 clutch is not engaged because of low oil pressure.

• No. 7 clutch is not engaged because of discs and plates that have too much wear.

• No. 7 clutch is not engaged because of broken components.

• malfunction of the transmission control.

The transmission does not operate in FIRST, THIRD or FOURTH speeds but the transmission operates in REVERSE, SECOND, FIFTH, SIXTH, SEVENTH, and EIGHTH speeds.

Probable Cause

• No. 6 clutch is not engaged because of low oil pressure.

• No. 6 clutch is not engaged because of discs and plates that have too much wear.

• No. 6 clutch is not engaged because of broken components.

• malfunction of the transmission control.

The transmission does not operate in SECOND, FIFTH, or SIXTH speeds but the transmission operates in REVERSE, FIRST, THIRD, FOURTH, SEVENTH, and EIGHTH speeds.

Probable Cause

• No. 5 clutch is not engaged because of low oil pressure.

• No. 5 clutch is not engaged because of discs and plates that have too much wear.

• No. 5 clutch is not engaged because of broken components.

• malfunction of the transmission control.

The transmission does not operate in SEVENTH or EIGHTH speeds but the transmission operates in REVERSE and FIRST through SIXTH speeds.

Probable Cause

• No. 4 clutch is not engaged because of low oil pressure.

• No. 4 clutch is not engaged because of discs and plates that have too much wear.

• No. 4 clutch is not engaged because of broken components.

• malfunction of the transmission control.

The transmission does not operate in FOURTH, SIXTH, and EIGHTH speeds but the transmission operates in REVERSE, FIRST, SECOND, THIRD, FIFTH, and SEVENTH speeds.

Probable Cause

• No. 2 clutch is not engaged because of low oil pressure.

• No. 2 clutch is not engaged because of discs and plates that have too much wear.

• No. 2 clutch is not engaged because of broken components.

• malfunction of the transmission control.

The transmission does not operate in THIRD, FIFTH, and SEVENTH speeds but the transmission operates in REVERSE, FIRST, SECOND, FOURTH, SIXTH, and EIGHTH speeds.

Probable Cause

• No. 3 clutch is not engaged because of low oil pressure.

• No. 3 clutch is not engaged because of discs and plates that have too much wear.

• No. 3 clutch is not engaged because of broken components.

• malfunction of the transmission control.

The torque converter gets hot.

Probable Cause

• The oil level in the transfer gear case is low.

• The water level in the engine radiator is low.

• There are restrictions in the oil cooler or the oil lines.

• There is excessive operation of machine at stall speed or near stall speed.

• There is excessive oil in the torque converter housing because of excessive leakage inside the torque converter.

• There is not enough oil in the torque converter.

• The pressure setting for the torque converter outlet relief valve is set too low.