0304573 JOHNSON SCREW,Idle adjustment

Table 1
Diagnostic Codes Table
CDL Code and Description Conditions which Generate this Code System Response
168-2 Electrical System Voltage : Erratic, Intermittent, or Incorrect The Electronic Control Module (ECM) has detected a supply voltage of less than 6 V while the engine is running. The code is logged.
The alarm output is activated.
336-2 Engine Control Switch : Erratic, Intermittent, or Incorrect The ECM has detected a combination of inputs for the engine control switch that is invalid. The code is logged.
The alarm output is activated.
The shutdown output is activated.
The engine is shut down. Electrical power from the batteries is supplied to the following components:
Master Electronic Control Module (ECM)
Slave ECM (20 cylinder engines only)
Fuel metering valve
Throttle actuator
Compressor bypass actuator
Control panel for the Advisor moduleThe cause of an intermittent problem with the power supply can occur on either the positive side or the negative side of the power supply.The 24 VDC power supply for the engine can be provided by a battery or by an electrical power supply. The minimum requirement for the power supply is 22 VDC at 16 A.The components are electrically protected by three fuses that are located in the junction box. The junction box is mounted to the left side of the engine.Both the master ECM and the slave ECM receive keyswitch power from the engine control switch. Terminal location P1-70 and P3-70 are used for this purpose. Keyswitch power is available at this terminal when the engine control switch is in the START position, the STOP position, or the AUTO position. When the master ECM and slave ECM detects battery voltage at the keyswitch input, the control modules will power up. When battery voltage is removed from this input, the control modules will power down.Note: If replacement of the engine control switch is necessary, be sure to use replacement parts that have been approved by Caterpillar. The use of aftermarket parts may cause adverse conditions during engine starting and/or engine operation.The fuel metering valve, the actuator for the bypass valve, and the throttle actuator receive electrical power via dedicated fuses at the junction box.A digital return at terminal location P1-31 is used as a ground source by the engine control switch. The position of the switch is reported to the master ECM via terminal locations P1-61, P1-62, and P1-64. The engine control switch provides a ground path to the appropriate terminal location as the position of the engine control switch is changed. The ECM input circuitry monitors the position of the engine control switch by detecting the ground source at these terminal locations. This information is used by the ECM for the engine state control.A problem with the electrical power supply is probably caused by a problem with the batteries. The next likely cause is a problem in the harness or in a connector. The least likely cause is a problem with the ECM.
Illustration 1 g06471720
Schematic for the electrical power supply for 8, 12, and 16 cylinder engines
Illustration 2 g03082556
Schematic for the electrical power supply for 20 cylinder engines
Illustration 3 g01697374
Locations of the junction boxes for the electrical power supply (left front engine view)
(1) ECM junction box
(2) Engine junction boxTest Step 1. INSPECT THE ELECTRICAL CONNECTORS AND THE WIRING
Turn the engine control switch to the OFF/RESET position. Remove the electrical power from the engine.
Illustration 4 g01696396
Locations of the components at the ECM junction box that are associated with the electrical power supply (typical left side engine view)
(3) J1/P1 master ECM connectors
(4) Control harness connector
(5) Power harness connector
Illustration 5 g01697380
Locations of the components at the engine junction box that are associated with the electrical power supply (typical left side engine view)
(6) Engine harness connector
(7) Engine interface connector
Thoroughly inspect connectors (3), (4), (5), (6), and (7). Refer to Troubleshooting, "Electrical Connectors - Inspect" for details that are related to inspection of the electrical connectors.
Illustration 6 g01637243
Terminal locations at the engine junction box that are for the electrical power supply
(8) 10 amp fuse for the throttle actuator (fuse 4)
(9) 10 amp fuse for the fuel metering valve (fuse 5)
(10) 10 amp fuse for the compressor bypass actuator, electronic control module, advisor monitor display, and the service tool (fuse 6)
(11) Jumper terminal for the +Battery to fuse 6 (terminal 3)
(12) Connection for the +Battery to the ECM (terminal 4)
(13) Connection for the +Battery to the service tool connectors (terminal 5)
(14) Connection for the keyswitch power that is for the ECM, the exhaust temperature scanner, and the voltage load protection module (terminal 8)
(15) Connection for the −Battery to the compressor bypass actuator (terminal 9)
(16) Connection for the −Battery to the ECM and to the throttle actuator (terminal 10)
(17) Connection for the −Battery to the service tool connectors, to the fuel metering valve, and to the voltage load protection module (terminal 11)
(18) Connection for the keyswitch to the exhaust temperature scanner and to the voltage load protection module (terminal 12)
Illustration 7 g01701015