GUARD AS 2068961 - Caterpillar

System Operation Description:Use this procedure to troubleshoot the following diagnostic codes:
Table 1
CDL Code and Description    
318-3 Right Detonation Sensor voltage above normal    
318-4 Right Detonation Sensor voltage below normal    
319-3 Left Detonation Sensor voltage above normal    
319-4 Left Detonation Sensor voltage below normal    One detonation sensor is threaded into the cylinder block for each cylinder bank. The Electronic Control Module (ECM) supplies 8 VDC in order to power the sensors. The detonation sensors provide electrical signals to the ECM that indicate mechanical engine vibrations. The signal is amplified and the signal is filtered by the ECM. 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 ECM monitors the signals in order to determine the presence and the severity of the detonation. If detonation occurs, the ECM retards the timing in order to stop detonation from occurring. The ECM can retard the timing by as little as 0.1 degree for light detonation. The ECM can retard the timing by a maximum of 6 degrees for severe detonation. If retardation of the timing does not sufficiently limit the detonation, the engine is shut down.A proportional strategy is used to advance the timing out of detonation retard. The rate of advance depends on the severity of the detonation. If the detonation level is low, the advance rate is faster. The fastest rate of timing advance out of detonation is 2 degrees per minute.The ECM will diagnose the detonation sensor signal circuit that is shorted to −Battery, +Battery, or an open circuit.While the harness connector is disconnected, the voltage on the signal wire may measure 0 VDC. Note the internal ECM circuitry for the detonation sensors do not utilize any pull up resistors. Therefore, a pull up voltage will not be present on the signal wire of the detonation sensor.The 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 ECM will shut down the engine. Detonation protection is disabled when the engine speed is less than 250 rpm.The most likely cause of a diagnostic code is a poor connection or a problem in a wiring harness. The next likely cause is a problem with a sensor.This troubleshooting procedure may generate additional diagnostic codes. Correct the cause of the original diagnostic code prior to troubleshooting other codes. Clear the diagnostic codes after the problem is resolved.
Illustration 1 g01250401
Schematic for the detonation sensorsTest Step 1. Inspect the Electrical Connectors and Wiring
Set the engine control to the OFF/RESET position.
Illustration 2 g01393685
(1) J2/P2 ECM connectors
Illustration 3 g01393702
Location of the detonation sensor that is for the right cylinder bank (typical right side engine view) (2) Detonation sensor (right cylinder bank)
Illustration 4 g01395916
Location of the detonation sensor that is for the left cylinder bank (typical left side engine view) (3) Detonation sensor (left cylinder