Home » GM 6.5 » GM/Detroit 6.5L – Engine Management – DIAGNOSTIC REQUEST – Component and Circuit Operation

GM/Detroit 6.5L – Engine Management – DIAGNOSTIC REQUEST – Component and Circuit Operation

DATA LINK CONNECTOR (DLC) TERMINAL “B” — DIAGNOSTIC REQUEST
When grounded to terminal “A”, terminal “B” allows the MIL to flash diagnostic trouble codes.

DATA LINK CONNECTOR (DLC) TERMINAL “G ” — FUEL PUMP
DLC terminal “G” allows technicians to enable the fuel pump to test for proper pump operation. CKT 490 from terminal “G” connects to fuel pump relay pin “C.” Powering terminal “G” activates the fuel pump. During engine operation, voltage at terminal G should be within 1.5 volts of battery voltage. If it isn’t, an oil pressure circuit problem should be suspected.

DATA LINK CONNECTOR (DLC) TERMINAL “M” — SERIAL DATA
Terminal “M” at the DLC is the serial data link for fast-baud PCMs. Serial data is a series of rapidly changing voltage signals pulsed from high to low voltage. These signals are typically 5 volts. Through terminal “M,” a “Scan” tool can read the serial data being sent between various components of the system being tested.

DTC 51 — “PROM Error (Faulty or Incorrect PROM)”
DTC 51 identifies a fault in the Programmable Read-Only Memory (PROM) portion of the PCM. PROM contains engine calibration information specific to the vehicle, model year, and emissions. The PROM also contains information used to allow fuel delivery if other parts of the PCM are damaged.

DTC 54 — “PCM Fuel Circuit Error”
DTC 54 indicates a fault in the fueling circuit fo the PCM. If a DTC 71 is also stored with DTC 54, diagnosis should begin with DTC 71.

MALFUNCTION INDICATOR LAMP (MIL)
The MIL alerts the driver to conditions requiring service. The MIL lamp receives ignition power through the ignition switch on CKT 39. The PCM turns the SES on by applying voltage on CKT 419.

DTC 46 — “MIL Circuit Fault”
DTC 46 sets when the PCM sees incorrect voltage at terminal E5.

“SERVICE THROTTLE SOON” (STS) LAMP
The “Service Throttle Soon” (STS) alerts the driver to APP module conditions requiring service. The STS does not display diagnostic trouble codes.
The STS lamp illuminates at key “ON” for 2 seconds as part of its bulb and system check. The lamp turns “OFF” at engine startup. If the STS lamp remains illuminated, the self-diagnostic system has detected a problem.

 

 

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