Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 260 (ENGINE CONTROLS - SELF-DIAGNOSTICS)DIAGNOSTIC TESTSDTC P0386: CRANKSHAFT POSITION SENSOR B CIRCUIT PERFORMANCETEST DESCRIPTION
1999 GMC Forward Control 5.7 R, Automatic
Test Description
1999 GMC Forward Control 5.7 R, AutomaticSECTION Test Description
WARNING: This page is about a different car, the 2003 Cadillac Seville and 2003 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
The numbers below refer to the step numbers in the diagnostic procedures.
- 2
During normal operation, the PCM uses the angle mode in order to determine engine position. In order to operate in this mode, the PCM must receive valid input from both CKP sensors. If the PCM detects a loss of CKP sensor "A" signal, the PCM switches to a Time "B" Mode using CKP sensor "B" input in order to determine engine position. If the PCM detects a loss of CKP sensor "B", the PCM switches to a Time "A" Mode using CKP sensor "A" input in order to determine engine position. If the PCM detects a loss of CKP sensor "A" signal DTC P0335 will set. DTC P0386 will only set if a problem with CKP sensor "B" occurs while in Time "B" Mode. DTC P0335 must be diagnosed first. - 6
To properly verify any repair to CKP sensor "A" harnesses/connectors, the system must be commanded to operate in Time "B" mode. This forces the PCM to use CKP sensor "B" to determine engine position. If the system is functioning normally, DTC P0386 should not reset.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.