FITTING 5B9916 - Caterpillar

System Operation Description:Use this procedure to troubleshoot any suspect problems with the circuits for the engine retarder solenoids.This procedure covers the following diagnostic codes:
121-05 Low/High Retarder current low
121-06 Low/High Retarder current high
122-05 Med/High Retarder current low
122-06 Med/High Retarder current highThe engine retarder solenoids are usually factory installed at Caterpillar and the switches are installed by the vehicle OEM. The Engine Control Module (ECM) directly drives the retarder solenoids, eliminating OEM installed relays and circuit protection. The ECM reads the status of the OEM installed engine retarder switches in order to determine the following modes of operation:
OFF
Low
Medium
HighOperation of the retarder solenoids is inhibited during undesirable engine operating conditions. All of the following conditions must be met in order to ensure the proper retarder operation regardless of the settings of the customer specified parameters:
Engine speed is above 800 rpm.
The "Accelerator Pedal Position" is less than eight percent.
The clutch pedal is released.Additional factors may affect retarder operation. The additional factors are based on the programming of certain customer specified parameters. Refer to Troubleshooting, "Customer Specified Parameters" for more information. The following parameters may affect retarder operation:
"Engine Retarder Mode"
"Auto Retarder In Cruise"
"Auto Retarder In Cruise Increment"
"Engine Retarder Minimum Vehicle Speed"
"Engine Retarder Minimum Vehicle Speed Type"
"Engine Retarder Delay"Note: If the "PTO Configuration" is programmed to "Cab Switches", to "Remote Switches", or to "Remote Throttle", the engine retarder is disabled whenever the PTO On/Off circuit is On.Trucks that are equipped with SAE J1939 systems may also control the engine retarder. For an Anti-Lock Brake System (ABS) that does not use SAE J1939 with the engine retarder solenoids, a relay may be connected into the retarder switch circuit in order to disable the engine retarder or a relay may be connected into the clutch switch circuit in order to disable the engine retarder.Note: If the vehicle is equipped with an ABS, the vehicle may have an additional relay in the switch circuit for the engine retarder switches or the clutch switch. This is installed so the ABS can turn off the engine retarder, if necessary. The relay should have normally closed contacts. The ABS cannot turn on the engine retarder. The Caterpillar ECM must still activate the retarder.Note: If the "Transmission Style" parameter is programmed to "Eaton Top 2", normal engine retarder operation can be inhibited by the ECM. Normal engine retarder operation can be inhibited by the ECM when the driver is attempting to make a shift in Top 2 mode in order to provide better control of torque during the process of shifting."Retarder Brake Test"The "Retarder Brake Test" is a diagnostic test that is available on the Caterpillar Electronic Technician (ET). Use the "Retarder Brake Test" to assist in troubleshooting problems in the circuit for the engine retarder. The ECM will only detect shorts in the circuit for the engine