MEFI Fuel Injection
TPS Circuit
The TPS and the MAP sensor share the 5 volt reference feed. The A/D converter on the 5 volt reference feed is used to detect whether the 5 volts is present or not. If the voltage is not there a “5v reference out of range” fault code. One possible cause of this fault is the 5 volt reference circuit being shorted to ground. The ECM watches the A/D converter on the signal wire. If the voltage goes too close to 0v, then a “TPS voltage low” fault is set. If the voltage goes too close to 5v, then the ECM sets a “TPS voltage high” fault. Remember, the fault codes are set by what voltage the ECM “sees” at the A/D converter. As an example, a TPS voltage low fault could be set by an open in the signal wire, a shorted signal wire, or an open in the 5 volt reference feed. A good quick check of the TPS circuitry is to disconnect the TPS and with a voltmeter check from cavity A to a known good ground. If the voltmeter measures 5 volts, then measure between cavities A and B. If the voltmeter still reads 5 volts, then the sensor return is good. Then short the 5 volt reference into the signal wire and read TPS Volts with a scan tool. If the scan tool reads 5 volts, then the signal wire is good and the ECM can read the voltage with the A/D converter.
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