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 83 (ENGINE CONTROLS - SELF-DIAGNOSTICS)DIAGNOSTIC TESTSDTC P0340: CAMSHAFT POSITION SENSOR CIRCUITDIAGNOSTIC PROCEDURES
1999 GMC Forward Control 5.7 R, Automatic
Diagnostic Procedures
1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2002 Saturn LW200, 2002 Saturn L200, and 2002 Saturn L100. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
If DTC P0336 is also present, diagnose that DTC first. See DTC P0336: CRANKSHAFT POSITION SENSOR CIRCUIT
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- Turn ignition off for 10 seconds. Using scan tool, monitor CALC COMPRESSION OUTPUT while starting engine. Continue to monitor parameter for 5 seconds after engine has started. If the last 4 digits are all zeros or ones, go to next step. If the last 4 digits are not all zeros or ones, problem is intermittent. See DIAGNOSTIC AIDS .
- Turn ignition on, engine off. Disconnect EI module. Using DVOM, measure voltage on EI module connector terminal "F" (Brown/White wire). If voltage is more than 0.2 volt, repair short to voltage in Brown/White wire between EI module and PCM. If voltage is not more than 0.2 volt, go to next step.
- Turn ignition off. Using DVOM, measure resistance between EI module connector terminal "F" (Brown/White wire) and ground. If resistance is less than 40 k/ohms, repair short to ground in Brown/White wire between EI module and PCM. If resistance is 40-60 k/ohms, go to next step. If resistance is more than 60 k/ohms, check for open or poor connection in Brown/White wire between EI module and PCM. If wire is okay, replace PCM.
- Reconnect EI module. Connect a diagnostic service probe to Brown/White wire. Start engine. Using a test light connected to battery voltage, touch, untouch and retouch test light to diagnostic service probe. PCM must see a transition from high to low, then back to high for this test to work. Using scan tool, monitor CALC COMPRESSION OUTPUT. If last 4 digits are all ones, go to next step. If last 4 digits are not all ones, check EI module connector. If connector is okay, replace EI module.
- If test light is on when touched to diagnostic service probe, replace EI module. If test light is off when touched to diagnostic service probe, replace PCM.
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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.