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HOMESERVICE MANUALSCHEVROLET1999SUBURBAN C2500, 6.5 FREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM - TESTS W/CODES - DTC P1537-U1193DTC P1555DTC P1555: EVO CIRCUIT FAULT (1.9L SATURN - DOHC)DIAGNOSTIC PROCEDURES
1999 Chevrolet Suburban C2500, 6.5 F

Diagnostic Procedures

1999 Chevrolet Suburban C2500, 6.5 FSECTION Diagnostic Procedures
  1. Install scan tool. Start engine. Using scan tool, command assist to FULL and NO while turning steering wheel. If power assist increases and decreases with commands, problem is intermittent. See DIAGNOSTIC AIDS . If power assist does not respond as commanded, go to next step.
  2. Monitor EVO feedback voltage as NO assist (maximum duty cycle) is commanded. If malfunction history indicates that feedback failed low (open/short to ground), go to step  4. If malfunction history indicates that feedback failed high (short to voltage in EVO control signal circuit), go to next step.
    3. NOTE: If PCM is faulty, ensure battery voltage is not present on diagnostic feedback circuit (No. 1295). Battery voltage on this circuit will damage new PCM.
  3. Turn ignition off. Disconnect PCM harness connector J1. Check voltage on both EVO solenoid terminals at PCM. If voltage reading is present, repair shorted circuit to EVO solenoid. If voltage reading is not present, replace PCM. Check circuit for evidence of short to battery voltage.
  4. Turn ignition off. Disconnect PCM harness connector J1. Check resistance between ground and EVO solenoid harness connector terminals J1D04 and J1D05. If resistance is less than 2 ohms, repair short to ground in circuit. If resistance is not less than 2 ohms, go to next step.
  5. Check resistance between EVO solenoid harness connector terminals. If resistance is less than 8 ohms, check circuits for being shorted to each other or shorted solenoid. If resistance is not less than 8 ohms, go to next step.
  6. If resistance is greater than 12 ohms, check for open in EVO solenoid circuit in fuse block, open EVO solenoid circuit between PCM and solenoid, terminal tightness or open EVO solenoid. If resistance is less than 12 ohms, check for terminal tightness or faulty PCM.
RENDER: 1.0x

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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.