TM 10-3930-675-24-1
ELECTRONIC CONTROL UNIT (ECU) INPUT VOLTAGE TROUBLESHOOTING
THIS WORK PACKAGE COVERS
Error Code 121 - Supply Voltage to Servo ECU (790)
Error Code 201 - Supply Voltage to Tophandler ECU
Failure
(791) Failure
Error Code 122 - Supply Voltage to Servo ECU (790)
Error Code 202 - Supply Voltage to Tophandler ECU
Failure
(791) Failure
Error Code 123 - 10V Reference Voltage for Servo ECU
Error Code 203 - 10V Reference Voltage for Tophandler
(790) Short Circuit Failure
ECU (791) Failure
INITIAL SETUP
References
References - Continued
ECS Attachment (A34652.0200) (WP 0048 00-23)
TM 10-3930-675-10
ECS Electrical Servo (A34648.0200) (WP 0048 00-
5)
Current Supply (A34738.0200) (WP 0048 00-31)
NOTE
Refer to WP 0004 00 for additional troubleshooting guidance, information, and illustrations that
locate critical components.
Refer also to illustrations at end of work package for component location.
Table 1. Error Code 121 - Supply Voltage to Servo ECU (790) Failure Troubleshooting Procedures.
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
Error Code 121 - Supply Voltage to Servo ECU 1. Check for emergency stop in
Disengage emergency stop
(790) Failure.
engaged position. (Multiple
button. (Error codes 121 and 201
error codes will display if the
will normally be one of the error
emergency stop button is
codes displayed.)
engaged during crank and
start.)
2. Check voltage (24V) at X154 a. If no voltage (24V) is found at
X154 pin 4, gain access to
pins 4 and 1 with the ignition
emergency stop switch and
ON (WP 0048 00-5).
check
connections
and
continuity (WP 0082 00) and
check continuity of wires 1541
and 1544 (WP 0048 00-5).
