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 MANUALSCHEVROLET1999SUBURBAN C2500, 6.5 FREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM - TESTS W/CODES - DTC P1537-U1193DTC P1634DTC P1634: IGNITION 1 SWITCH CIRCUIT (4.0L "G" BODY)DIAGNOSTIC PROCEDURES
1999 Chevrolet Suburban C2500, 6.5 F
Diagnostic Procedures
1999 Chevrolet Suburban C2500, 6.5 FSECTION Diagnostic Procedures
- Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
- Using scan tool, check if DTC P0560 is also present. If DTC P0560 is also present, diagnose this DTC first. If DTC P0560 is not present, go to next step.
- Note both the IGNITION 0 and IGNITION 1 displays on scan tool. Compare both voltage readings. If readings are within 1.5 volts of each other, go to next step. If readings are not within 1.5 volts of each other, go to step 5.
- Clear DTC using scan tool. Start and idle engine. After 10 seconds in DTC INFO mode, select FAIL THIS IGN. If DTC failed this ignition cycle, go to step 6. If DTC did not fail this ignition cycle, fault is not present. See DIAGNOSTIC AIDS .
- Check for open circuit or poor splice connection on circuit that has low voltage. Replace as necessary. If circuit is okay, fault is not present. DIAGNOSTIC AIDS .
- Check terminal contact at PCM harness connector C1 terminals No. 18 and 19. Repair as necessary. If terminal contacts are okay, go to next step.
- Replace PCM. Program replacement PCM using required equipment.
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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.