W T E C I I I E L E C T R O N I C C O N T R O L S T R O U B L E S H O O T I N G M A N U A L
Main code 64 indicates the ECU has detected a voltage signal from the retarder modulation request sensor
(consisting of a module and a retarder control device) in either the high or low error zone. These codes can be
caused by faulty wiring, faulty connections to the resistance module or retarder control device, a faulty resistance
module, a faulty retarder control device, or a faulty ECU. Power wire 124 and ground wire 135 for the retarder
modulation request sensor are a common power and ground with the TPS and OLS devices. A short-to-ground on
the common power wire causes a sensor failed low code for the other devices (codes 2112, and 1412). An open
or a short-to-ground on retarder modulation request sensor signal wire 164 results in a code 6412 only.
A TPS failure changes the status of the output retarder. The retarder is enabled by the Service Brake Status
(wire 137) when a TPS code is active (21XX). If a code 6340 is also active, the Service Brake Status (wire 137)
is ignored and the retarder will not work. Retarder response problems may not cause retarder modulation request
sensor diagnostic codes. If response questions occur, test the retarder control devices for proper voltage signals at
each of the percentage of retarder application settings. Table 58 contains the voltage measurements for each
devices application percentage and resistances measured across terminals A and C of the retarder request sensor.
Use test wiring harness J41339 when conducting voltage tests.
Active Indicator Clearing Procedure:
Before troubleshooting, read Paragraph 56. Also, check battery and ECU input voltages.
Intermittent connections or lack of battery-direct power and ground connections can cause this and
other electronic control codes.
Code 64 12 can be caused when the +5V power line (wire 124) is shorted to ground or open. Wire 124
also provides power for the OLS, TPS, sump temperature sensor, retarder temperature sensor, and
shift selectors and is present in all three ECU connectors..
1. Plug in the DDR and set to read retarder counts and percent (0 percent will be between 15 and 60
counts and 100 percent will be between 150 and 233 counts). A retarder request sensor failed high
code can be caused by a short-to-battery of either signal wire 164 or power wire 124 or an open on
ground wire 135. An open in the portion of the ground circuit common to the TPS and OLS devices
will also result in a code 2123 and a high fluid level reading. A retarder request sensor failed low
code can be caused by an open or short-to-ground on either signal wire 164 or power wire 124.
2. Isolate and repair any wiring problems found.
3. If no wiring or connector problems are found, check the retarder request sensor voltages for each
position on each of the retarder request sensors used on the vehicle. If two resistance modules are
used, disconnect one of them when measuring voltage signals from the other. If problems are
found, replace the resistance modules or retarder control devices.
4. If the problem persists, replace the ECU. If replacing the ECU corrects the problem, reinstall the
original (bad) ECU to confirm that the problem is in the ECU. If the original ECU now works, in-
spect the ECU connectors for any corrosion or damage which may cause an intermittent condition.
If the original problem recurs, reinstall the replacement ECU.
Retarder Modulation Request sensor failed Low (14 counts and below)
Retarder Modulation Request sensor failed High (232 counts and above)
CODE 63 XX INPUT FUNCTION FAULT