Tahoe CKP Breaks Starter

“Sometimes there’s a more complicated reason why a starter-housing will break and the flywheel ring gear teeth get ground off,” I said convincingly, switching the phone receiver to my other ear. “But my next-door neighbor says it’s probably just a bad starter,” insisted Brandon, one of my regular customers. “You’ll just have to trust me on this one,” I assured him. “Consider the additional check-out time as an insurance policy against future starter problems.” “Well, okay,” he replied. “You’ve always been right before – go ahead and check it out.”

As I hung up the phone and updated the revised estimate with Brandon’s approval information, I recalled seeing a late model Chevrolet Tahoe technical service bulletin (TSB) once that linked bad Crankshaft Position (CKP) sensors to various starter-related problems. Revisiting that particular TSB confirmed my suspicions. Here are the details:

Some 1998 to 2000 Chevrolet Tahoe models may exhibit any one or a combination of the following symptoms, which can be caused by a bad CKP sensor:

A diagnostic trouble code (DTC) P0338

Backfire during engine cranking or starting

“Kickback” during engine cranking or starting

“No” start

“Slow” or “hard” cranking or starting

“Grinding” or unusual noises during engine cranking or starting

Cracked or broken engine block at the starter boss

Broken starter drive housing

Broken or stripped teeth on starter flywheel ring gear

Cause:

A condition may exist that allows the CKP sensor to command up to 50 extra degrees of spark advance during engine cranking only. This in turn exposes the engine to higher than normal cylinder pressures, which may result in hard starting and starter system component-related damage.

Correction:

Inspect for the stored powertrain DTC code “P0338.” This DTC will NOT illuminate the “Malfunction Indicator Lamp”. If this code is stored, the CKP sensor MUST be replaced and the remaining components inspected for damage (engine block at the starter boss, the starter drive housing and the engine flywheel starter ring gear).

NOTE: When DTC code P0338 is set, failure to replace the CKP Sensor could result in repeated inoperative conditions of the starter or flywheel.

Removing CKP Sensor

NOTE: When installing or removing a CKP sensor, make sure the sensor is fully seated and held stationary in the front cover before tightening the hold down bolt. A sensor which is not seated may result in erratic operation and lead to the setting of false codes.

1. Remove the electrical connector.

2. Remove the sensor hold down bolt.

3. Remove the sensor from the timing cover.

4. Inspect the sensor O-ring for wear, cracks or leakage. Replace if necessary.

Installation Procedure

NOTE: Make certain that the CKP sensor mounting surfaces are clean and free of burrs before installing the CKP sensor.

1. Lube the CKP sensor O-ring with clean engine oil before installing.

2. Install the sensor into the timing cover.

3. Install the sensor hold down bolt and tighten bolt to 71 in. lbs. (8 Nm)

4. Install the electrical connector.

Using a diagnostic scan tool, we did retrieve a DTC P0338 trouble code, so a replacement of the bad CKP sensor was in order. When the repair was complete, we let the engine idle in the shop until it ran normally, which allowed the VCM to “re-learn” the new component. A subsequent test-drive verified that the vehicle performed normally.

Needless to say, Brandon was pleased and very grateful for the way we professionally handled the complete diagnosis and repair of his vehicle’s starter problem. “You guys are great. I can always trust you to do thorough job. A lot of shops might not have taken the time to investigate the root cause of my broken starter housing,” he remarked. That’s the kind of compliment we like to hear.