1999 GMC Jimmy OBD2

Hello,

Here are a few causes for the incomplete scan.

OBD2 (OBDII) Scan Test is Incomplete
The computer system or ECM, PCM (engine control module, powertrain control module) that controls your car is equipped with a basic operating program. This operating program is designed to control your engine, transmission, emissions, safety systems and more. If a scan has been performed by using a code scanner and a "scan could not be completed" code is retrieved further troubleshooting is necessary. Usually a trouble code P1000 or manufacturers equivalent. We have listed several reasons for this condition.

Stuck Engine Thermostat - If the engine thermostat has stuck open it forces the engine coolant to stay at too low causing the ECM/PCM to stay in open loop. This open loop creates a state of preprogrammed parameters were no diagnostic tests can be preformed. (The ECM/PCM is constantly waiting for the engine to heat up to operating temperature)

Shorted Oxygen Sensor/Coolant Sensor - The ECM/PCM relies on main sensors to operated, if one of these sensors is severely shorted it can cause the ECM/PCM to stay in open loop causing a code gathering incomplete trouble code.

Shorted Fuel Injector - If a fuel injector short circuits it can cause the engine not to run by shorting the injector driver. If the car doesn't run and a diagnostic trouble codes can be set for causing an code gathering incomplete trouble code like P1000