Chart 1 of 4

Diagnostic Chart Part 1:

Schematic 1:

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 "fuel disable password" to the ECM over the CAN bus. 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 CAN bus to the ECM. If the ECM password does not match the BCM password; or if the ECM does not receive a password from the BCM, it will allow the engine to start then stall within 4 seconds. The SECURITY telltale will flash for 10 minutes if the ECM receives no password, an incorrect password or a disable fuel command. If the password to the ECM is correct, the engine will operate normally. The password is sent continuously by the BCM to the ECM during run mode. If the password becomes lust 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 ECM passlock/security system DTCs P1630, P1631, P1632 or B1372
^ ECM internal fault DTCs

Make sure ECT, MAP and TP SENSOR readings on Scan tool with ignition On, engine Off look normal. MAP should be between 98-104 kPa (14-15 psi) with ignition On, engine Off. The ECT and IAT should be within 4°C (10°F) of each other if the vehicle has been sitting overnight. A skewed sensor reading may cause a hard/no start condition.

If no RPM from the crankshaft position (CKP) sensor is detected, spark and fuel will not be turned On. The signal from the CKP sensor is sent to the ECM. When engine is cranking, the Scan tool CKP ACTIVE COUNTER should continuously count up to 255 then reset to 0.

Check for a flooded engine.

These ECM fuses in the UHFB will cause a no start if open:
^ POWERTRAIN 10 amp
^ FUEL PUMP 10 amp
^ IGN 1/2 30 amp
^ IGN/INJ 15 amp
^ ECM/TCM 10 amp
^ ETC 15 amp
^ BCM 10 amp
^ BCM/Cluster 10 amp