Chart 1

Diagnostic Chart (Part 1 Of 4):

In order to correctly diagnose a no start condition, battery voltage must be above 11 volts and the engine must be cranking at normal cranking speed (above 200 RPM). Fuel level and fuel quality in the fuel tank should be checked (do not solely rely on the fuel gauge for level reading). When the engine is cranked, the BCM will check the password from the passlock sensor. If the password is not received within a certain amount of time or does the match the BCM password, the BCM will send a "disable fuel command" to the PCM over the Class II link. The SECURITY telltale will flash and the engine will not be allowed to start. If the passwords match, the BCM will send the password over the Class II link to the PCM. If the PCM password does not match the BCM password; or if the PCM does not receive a password from the BCM, it will allow the engine to start then stall within four seconds. The security telltale will flash for 10 minutes if the PCM receives no password, an incorrect password or a disable fuel command. If the password to the PCM is correct, the engine will operate normally. The password is sent continuously by the BCM to the PCM during run mode. If the password becomes lost or incorrect during the drive cycle, the vehicle will be allowed to start on succeeding ignition cycles without the aid of passlock and the SECURITY telltale will be On steady. This mode is called fail enable mode.

DIAGNOSTIC AIDS
DTCs that may cause a no start and should be diagnosed first:
^ U-type communication DTCs
^ BCM or PCM passlock/security system DTCs
^ P0231 or P0232 - Fuel pump relay coil circuit
^ P0351, P0352, P01351, or P01352 - Ignition Control (IC) circuit faults will cause mating cylinders 1-4 or 2-3 not to fire.
^ P0601, P0602, P0603, P0606, P1621 PCM internal hardware
^ P1635 - 5 volt reference circuit

Make sure the EGR valve is not stuck open by reading the EGR SENSOR voltage on Scan tool. Normal closed valve readings should be within 0.5 - 1.0 volts. Make sure the ECT, [1][2]MAP and TP SENSOR readings on Scan tool with ignition On, engine Off look normal. MAP should be between 98-102 kPa with ignition On, engine Off. The ECT and IAT should be within 4°F of each other if the vehicle has been sitting overnight.

If no RPM from the crankshaft position sensor is detected, spark and fuel will not be turned On. When engine is cranking, the Scan tool CMP RESYNC counter should count up to 14 then reset to 0 when #4 cylinder is on TDC compression.

Check for a flooded engine.

These fuses in the UHFB will cause a no start if open:
^ PCM B 10 amp
^ PCM 1 10 amp
^ I/P Batt 30 amp
^ EIS 10 amp
^ INJ 10 amp

These fuses in the IPFB will cause a no start if open:
^ Body Computer 10 amp
^ Ignition 1 10 amp
^ Fuel Pump 10 amp