12 - Cylinder Contribution Tests

12. Cylinder Contribution Tests





Purpose:
To test individual cylinders and injectors to determine if all are contributing equally to engine performance.

NOTE: Only California vehicles will set a Continuous Misfire DTC. Both 49-state and California vehicles will set a KOER Cylinder Contribution Self Test code for a low or non-contributing cylinder. If any CCT or misfire DTCs are set, go to Pinpoint Test NA to diagnose the fault. NA - Injector Driver Circuit Operation

Recommended Procedure:
The A/C must be OFF and engine oil temperature above 21°C(70 °F) to run Cylinder Contribution Self Test. This test will determine if all cylinders are contributing equally to engine performance. The PCM will test all eight cylinders continuously during the test; there is no change in engine speed or operation that can be detected by the technician. The test checks for cylinder-to-cylinder decrease in speed and sets a code if the decrease is too high. The test consists of three portions. Each portion runs for 20 seconds. The first test checks for a badly missing injector or cylinder with no compression, and the second and third tests check for weak injectors or low compression cylinders. A fault must be present at the time of testing for the KOER Cylinder Contribution Self Test to detect a fault, so the engine operating condition at which the idle is worst will produce the best test results. For automatic transmission vehicles, the best results are reached with the parking brake set and the transmission in DRIVE. If a fault is detected, a Diagnostic Trouble Code (DTC) will be output on the data link at the end of the test when requested by a scan tool. Only a hard fault code (DTC) will be displayed.

Possible Causes:
Failing this test could indicate mechanical engine problems such as:
- broken compression rings
- leaking or bent valves
- bent push rods
- bent connecting rods
- damaged rocker arms
- faulty injector assembly

If the base engine condition meets specifications, the injector may not be functioning correctly and will need replacement. The solenoid and wiring should have been checked in earlier tests. Verify KOEO Injector Electrical Self Test passed.

Tools Required:
New Generation Star Tester 007-00500 or equivalent