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Illustration 1 g00914624
Arrangement of the detonation sensors (A-E) Detonation sensorsThe master Electronic Control Module (ECM) and the slave ECM supply 8 VDC to each detonation sensor. The detonation sensors provide electrical signals to each ECM that indicate mechanical engine vibrations. The signals are amplified and the signals are filtered. The frequency of the signal corresponds to the mechanical frequency of the vibrations. The amplitude of the signal is proportional to the intensity of the vibrations.The master ECM monitors the detonation sensors on the left side of the engine. The slave ECM monitors the detonation sensors on the right side of the engine. The signals are monitored in order to determine the presence and the severity of the detonation. The master ECM can retard the timing of the cylinders on the left side of the engine in order to limit detonation levels. The slave ECM can retard the timing of the cylinders on the right side of the engine in order to limit detonation levels. The timing may be retarded for a single cylinder or for more than one cylinder. The timing may be retarded for all of the cylinders, if necessary. If retardation of the timing does not sufficiently limit the detonation, the master ECM will shut down the engine.An ECM can retard timing by as few as three degrees for light detonation levels. The timing can be retarded up to six degrees for severe detonation. For most applications, the minimum allowable actual timing is ten degrees BTC (five degrees BTC for propane operation). A proportional strategy is used for advancing the timing after the timing has been retarded. The rate of advance is based upon the level of detonation. The rate is faster for lighter detonation. The fastest rate of proportional timing advance is one degree per minute.Each ECM will diagnose the detonation sensors for a signal that is shorted to the −battery side, the +battery side, or an open circuit. To avoid detecting vibrations that are not related to detonation, each ECM only monitors a detonation sensor when one of the pistons that is monitored by that sensor is between 5 degrees after top center and 40 degrees after top center on the power stroke. Therefore, the "Block Tap" method of testing the detonation sensors does not work for the G3500B Engine.An input from a detonation sensor that is diagnosed by an ECM as "open/shorted to +battery" may measure 0 VDC on a voltmeter. This is caused by the lack of pull up resistors in the detonation sensor's circuits inside the ECM.Each ECM also supports related event codes when the levels of detonation warrant a reaction from the ECM. If the timing has been retarded by the maximum amount and the level of detonation remains high, the master ECM will shut down the engine. Detonation protection is disabled when the engine speed is less than 250 rpm.Logged diagnostic codes provide a historical record. Before you begin this procedure, use the Caterpillar Electronic Technician (ET) to print the logged codes to a file.The most likely causes of the diagnostic code are a poor connection or a problem in a wiring harness. The next likely cause is a problem with a sensor. The least likely cause is a problem with an ECM.The troubleshooting procedure may generate additional diagnostic codes. Keep your mind on correcting the cause of the original diagnostic code. Clear the diagnostic codes after the problem is resolved.
Illustration 2 g00993497
Schematic for the detonation sensorsTest Step 1. Inspect the Electrical Connectors and Wiring
Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.Note: For the following steps, refer to Troubleshooting, "Inspecting Electrical Connectors".
Illustration 3 g00890369
Terminal box for the master ECM (1) J2/P2 connectors for the master ECM (2) J11/P11 connectors for the detonation sensors on the left side of the engine (3) 16 amp circuit breaker
Illustration 4 g00902236
Terminal box for the slave ECM (4) J4/P4 connectors for the slave ECM (5) J21/P21 connectors for the detonation sensors on the right side of the engine
Thoroughly inspect each of the following connectors:
Master ECM J2/P2 connectors
J11/P11 connectors on the terminal box for the master ECM
J4/P4 connectors for the slave ECM
J21/P21 connectors on the terminal box for the slave ECM
Connectors for each of the detonation sensors
Check the torque of the Allen head screw for the ECM connectors. The proper torque is 6 1 N m (55 9 lb in).
Illustration 5 g00985646
Harness side of the side of the master ECM P2 connector (P2-36) Signal for cylinders 2 and 4 (P2-37) Signal for cylinders 6 and 8 (P2-38) Signal for cylinders 10 and 12 (P2-39) Signal for cylinders 14 and 16 (P2-44) Signal for cylinders 18 and 20 (P2-54) Return (P2-55) Return (P2-56) +8 V supply (P2-57) +8 V supply
Illustration 6 g00902248
Harness side of the side of the P11 connector (J11-B) Signal for cylinders 2 and 4 (J11-C) Signal for cylinders 6 and 8 (J11-D) Signal for cylinders 10 and 12 (J11-G) Signal for cylinders 14 and 16 (J11-H) Signal for cylinders 18 and 20 (J11-A) Return (J11-E) Return (J11-J) +8 V supply (J11-F) +8 V supply
Illustration 7 g00985646
Harness side of the P4 connector for the slave ECM (P4-36) Signal for cylinders 1 and 3 (P4-37) Signal for cylinders 5 and 7 (P4-38) Signal for cylinders 9 and 11 (P4-39) Signal for cylinders 13 and 15 (P4-44) Signal for cylinders 17 and 19 (P4-54) Return (P4-55) Return (P4-56) +8 V supply (P4-57) +8 V supply