SYS.OK|MANUAL.DB● LIVE
HOMESERVICE MANUALSCHEVROLET1996CHEVY VAN G30, VAN CARGO EXTENDED, 6.5 YREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - TESTS W/CODES - 6.5L DIESEL.DIAGNOSTIC TROUBLE CODE CHARTSCHART A-2, NO DATA LINK CONNECTOR (DLC) DATA, WILL NOT DISPLAY DTC 12 OR MIL ON STEADY (4L80-E W/ TCM)
1996 Chevrolet Chevy Van G30, Van Cargo Extended, 6.5 Y

Chart A-2, No Data Link Connector (DLC) Data, Will Not Display DTC 12 Or Mil On Steady (4L80-E W/ TCM)

1996 Chevrolet Chevy Van G30, Van Cargo Extended, 6.5 YSECTION Chart A-2, No Data Link Connector (DLC) Data, Will Not Display DTC 12 Or Mil On Steady (4L80-E W/ TCM)

MIL should be on when engine is off and ignition is on. Switched battery voltage is supplied to MIL. The TCM turns light on by providing a ground path through the MIL (SERVICE ENGINE SOON) control circuit. With diagnostic terminal grounded, MIL should flash DTC 12, followed by any other DTC stored in memory. A steady light on indicates a short to ground in the MIL (SERVICE ENGINE SOON) control circuit or an open in the diagnostic request circuit.

NOTE: Test numbers refer to numbers on diagnostic chart.
  1. If there is a problem with TCM that causes scan tester not to read serial data, TCM should not flash DTC 12. If DTC 12 does flash, ensure scan tester is functioning properly (on another vehicle). If scan tester is functioning properly, and serial data circuit is okay, PROM or TCM may be at fault for the NO DLC symptom.
  2. If light goes off when PCM connector is disconnected, MIL (SERVICE ENGINE SOON) control circuit is not shorted to ground.
  3. This step checks for an open in the diagnostic request circuit.
  4. At this point, MIL wiring is okay. Problem is a faulty PROM. If DTC 12 does not flash, TCM should be replaced using original PROM. Replace PROM only after trying a TCM. A defective PROM usually is an unlikely cause of problem.
Fig 1: Chart A-2 Schematic (4L80-E W/ TCM) No DLC Data, Will Not Display DTC 12 Or MIL On Steady
G95E26934
RENDER: 1.0x

NO RELATED

Recommended Tools & Savings

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Affiliate disclosure: We may earn a commission at no extra cost to you.

Shop Manual-Ready ToolsFree Quote CheckQuote Shield Pro

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.