GM/Detroit 6.5L – Engine Management – FUEL CONTROL – “SERVICE THROTTLE SOON” (STS) LAMP

Description
The “Service Throttle Soon” (STS) in the instrument panel alerts the driver to conditions in the accelerator pedal position (APP) circuit that require attention.

Under normal operation, the STS lamp illuminates when the ignition is “ON” and the engine is “OFF.” The lamp comes “ON” for approximately 2 seconds at key “ON” and turns “OFF” when the engine is started. If the light remains illuminated after the engine has started, a problem may exist in the STS or APP circuits. The appropriate diagnostics should be followed as directed by the OBD System Check.

STS Circuit Operation
The PCM illuminates the “Service Throttle Soon” lamp by providing a ground on CKT 960 at the module (figure 5-34). The “Service Throttle Soon” lamp receives battery power through the ignition switch on CKT 39.

DTC 49 — ‘“ Service Throttle Soon’ Lamp Circuit Fault”
DTC 49 sets when the PCM sees incorrect voltage at terminal A5. DTC 49 could also be caused by an open or short to ground in CKT 960 to the PCM or an open in CKT 39 from the ignition switch, or by a faulty bulb or fuse.

 

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