Mil On. Tach Inoperative. Codes P0341, P0215, P1689, P1690. Check Cam Sensor Operation.;When codes p0341, p0215, p1689 and p1690 set do p0341 diagnostics. You may find that sensor voltages (map, apps, oil pressure, cam and crank sensors) on a 24 valve diesel engine differ from what you may be used to seeing. The reference voltage should be about 5 volts, the signal wire 0 volts and sensor ground. On 2001 & 2002 models with P0341, p0215, p1689 and P1690 setting or the tachometer is dropping out, monitor the cam sensor (CMP) signal with the DRBIII. Verify the signal is constant/steady. Inspect the cam sensor wiring. Repair wiring or replace the sensor as needed. If cam sensor and circuit check ok, inspect for excessive camshaft endplay. The end play specification is 0.006 -0.010 inch. If camshaft endplay is out specification, the camshaft gear assembly must be replaced. Reference the 2002 powertrain manual, pg #169. Test #1, measure the AC noise on battery voltage to ECM, is the voltage above 25mVrms? (Possible electrical noise from the Transfer pump). If codes 1690 and or 1689 are setting load test the injection pump power and ground at the injection pump connector using a head light as a load.