1995 Ford Mustang 6-cylinder, OBD2 fault code PO1020. Vehicle last serviced in January/February 2024 at 189,000 miles. A new Throttle Position Sensor (TPS) was installed by the previous owner. The PO1020 code clears when the engine is turned off but returns consistently after restarting. Despite the TPS replacement, the issue persists. Seeking advice on potential root causes and diagnostic steps.
I don't have direct experience with this, but I'd like to understand better. Can you explain how the throttle position voltage works and why it might trigger PO1020? Thanks for the insight—Maurto
When the key is on but the engine is off (KOEO), the Powertrain Control Module (PCM) monitors throttle position voltage. If readings fall outside expected ranges, it triggers code PO1020. You can measure this directly using a digital multimeter (DMM). The signal wire should show approximately 0.75V to 1V at idle. Any reading below 0.5V may trigger PO1120 instead. Always inspect for corrosion, damaged wires, or loose connections in the TPS harness. Back-probing the connector with a DMM is recommended if possible. ATB—Aeroman.
Thanks for the detailed explanation! I'll check this tomorrow and update accordingly. This helps a lot—appreciate it, Maurto.
Aeroman59 wrote: Basically, with Key on Engine off, the throttle position (angle or voltage ) is measured by the PCM. If the voltage is outside the expected range, the computer throws that code. You can measure this voltage or have it tested , but check for corrosion or damaged/shorted wires or loose pins at the connector. If you are able to back probe the connector with a DMM the signal wire should give approx .75V to 1v at idle, anything lower than .5V will throw po1120. ATB Aeroman. Thanks, I will check this tomorrow and let you know. Very much appreciated Maurto
This is a common issue with older Mustangs—especially those with modified or tampered throttle systems. Check if the throttle cable has been altered or improperly adjusted. At idle, the voltage should read approximately 1 volt; at Wide Open Throttle (WOT), it should be around 4–5 volts. Always perform this test with the engine off (KOEO). Good luck—Aeroman.