Error Code P1120

97 Mercury Sable 150 K

The scan tool translates the code as a Fuel Metering issue. Would anyone haapen to know what would cause this code to show up? I am thinking that I need new plugs / wires but would like it if someone could conferm that the issue may relate to that.

If you would like the factory diagnostic procedure for that code in PDF format, send me a private message with an e-mail address for you that can accept attachments and I'll send it your way.

-Rod

P1120 is mfg code and it says "Throttle Position Sensor out of range (Low Ratch)" which means it is your Throttle Position sensor that is malfunctioning.
Check for electrical interference first: aftermarket radio, power inverter, police scanner, cb radio, cellphone & hands free headset, Audio capacitors, wireless radio transmitter ect...

The sensor itself is pretty easy to check and only runs at $40 which makes it pretty cheap to replace in the area of Ford sensors.

I actually have no clue how to test one without a dedicated tester, but my best guess without looking at the sensor would be to use a tachometer and a multimete. Monitor the tachometer and the voltage by slowly acclerating watch out for the any sudden surges or drops in voltage.................

Yeah just get Rod to send you the test procedure or go spend the 800 on a test kit.

A multimeter and steady foot are really all that is needed to test a TPS. A TPS is just a specially housed potentiometer - three wires, one for ground, one for reference voltage, and one for the wiper sets up a voltage divider. If you monitor with the multimeter in resistance across the wiper to one of the other terminals, then very slowly and linearly step down on the throttle pedal, the resistance should increase or decrease linearly (depends on if you are on ground or reference lead) as the throttle is opened and closed. If the resistance drops or jumps during a linear application of the throttle, then the TPS has a bad spot in it.

There is more to diagnosing the P1120 code than that, but that is a quick description on testing a TPS using tools that any DIY'er should have available.

-Rod

I'm going to replace the sensor and see if it helps. My check engine light has turned off on its own. Is an intermitant problem and decreased gas milage consistent with a bad TPS?

I would not expect a faulty TPS to have an intermittant code since once the resistive element goes bad, it is bad. Loose connections, or connections that lost their sealing ability and allow moisture/condensation in could certainly cause an intermittant. A dirty Mass AirFlow (MAF) sensor, out of range coolant temperature sensor, nearly plugged air filter, or Intake Air Temperature (IAT) sensor could all possibly give an intermittant code and have quite an effect on fuel economy as well.

-Rod

Per the 1998 Ford factory service manual:
Diagnostic Trouble Code (DTC) P1120 indicates the TP signal is within the Self-Test range but below the closed throttle position range of 3.43% to 9.80% (0.17 to 0.49 volt).

Possible causes:

-- Frayed wires.

-- Corrosion on TP sensor, PCM or harness connectors.

-- VREF harness opens or shorts.

-- Damaged TP sensor.

-- Damaged PCM.

The full diagnostic procedure is on its way to you via e-mail per your private message request.

-Rod

Thanks!