1999 Chevrolet Tahoe P1345 Code: Diagnosis and Fix After Crankshaft Position Sensor Replacement
My 1999 Chevrolet Tahoe has been experiencing intermittent starting issues for approximately one month. It would run normally one day, then the next night it would fail to start and sound like it was out of time. After letting it sit overnight, I managed to get it started again, but only for about a week before it began missing under cold conditions—running fine when warm. At that point, the check engine light illuminated with a multi-cylinder misfire and O2 sensor fault codes. The truck then stopped starting entirely, though it would restart after a few days. I recently replaced the crankshaft position sensor (crank sensor) in an attempt to resolve the issue. However, since the replacement, the vehicle has not started for four days. When attempting to start, it backfires through the throttle body. I'm now concerned that the new sensor may be defective or improperly installed. Given the age of this truck and its GM platform, I suspect potential mechanical issues such as lateral crankshaft movement due to wear in the thrust bearing—some older GM engines require a shim under the crank sensor to compensate for increased play under load. Additionally, I'm wondering if the distributor is still out of time or if there's damage to the reluctor ring behind the timing cover. The fact that it backfires without starting suggests either weak spark or incorrect ignition timing. I would appreciate any guidance on how to verify these issues using a scan tool and sensor readings (such as cam and crank position differences).
Good morning. First, let's lock this thread to avoid confusion with another post. Did the truck stop starting immediately after replacing the crankshaft position sensor? If yes, that suggests either a defective sensor or improper installation. Many GM trucks from the early 2000s develop increased lateral play in the crankshaft thrust bearing over time—this can cause timing issues even if the engine appears to run fine. A shim is often required under the sensor to maintain proper signal alignment when under load. If the intake was recently removed, this could also point to a distributor that's out of time or possibly has a bent shaft or seized components. If the truck started briefly after replacement but then failed to restart, it may indicate deeper timing issues unrelated to the sensor itself.