DTC P1120. Cadillac Catera 2001

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 2001 🢒 Catera 🢒 Body and Accessories 🢒 Wiring Systems 🢒 DTC P1120

Circuit Description

The throttle position (TP) sensor is part of the throttle body assembly. The TP sensor is actually 2 individual sensors within one housing. The TP sensor 1 is the main input to the engine control module (ECM) for actual throttle positioning. Each of the TP sensors share a common 5-volt reference circuit and a reference ground circuit. The 5-volt reference circuit is also shared with accelerator pedal position (APP) sensor 2. The 5-volt reference voltage is supplied on 2 separate ECM terminals, but the terminals are connected internally to the same voltage supply. The TP sensor 1 signal circuit is pulled up near 5 volts in the ECM and the signal circuit for TP sensor 2 is referenced to ground. This causes each TP sensor to have opposite functionality. The TP sensor 1 signal voltage increases as the throttle opens, from below 1.0 volt at 0 percent throttle to above 4.0 volts at 100 percent throttle. The TP sensor 2 signal voltage decreases from around 4.0 volts at 0 percent throttle to below 1.0 volt at 100 percent throttle.

Conditions for Running the DTC

The battery voltage is more than 7 volts.

Conditions for Setting the DTC

•	The TP sensor 1 voltage is less than 0.195 volts or more than 4.6 volts.

•	The difference between TP sensor 1 and TP sensor 2 is more than 13 percent.

•	One of the above conditions is met for 140 ms (0.140 seconds).

Action Taken When the DTC Sets

•	The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

•	The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC

•	The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

•	A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

•	A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

•	Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

The ECM compares the signal of each of the throttle position sensors to each other throughout the entire range of the throttle plates. The ECM also compares the signal of the throttle position sensors to other sensors when the engine is running to determine if the sensor readings are correct. Clear the DTCs and actuate the throttle through the entire range with the ignition ON and the engine OFF and also with the engine running. If the DTC resets, check all of the circuits to the throttle position sensors for high resistance. Resistance as low a 2 ohms in the TP sensor circuits can affect the operation of the sensors. Test the reference ground circuit of the TP sensors for a short to ground. The reference ground circuit is provided by the ECM and an external short to ground will affect the operation of the sensors. The reference ground is shared with other components so any faults on this circuit can affect the operation of the entire engine controls system. Refer to Circuit Testing in Wiring Systems.

With the ignition ON and the engine OFF, view the TP sensor 1 and the TP sensor 2 with a scan tool. Slowly depress the accelerator pedal, the voltage on TP sensor 1 should increase steadily from 0.7 volt to about 4.2 volts. TP sensor 2 should move opposite from above 4.2 volts to about 0.6 volt. If one sensor value changes and the other does not, inspect the sensor circuits for high resistance or shorts. If the circuits are OK, replace the throttle body assembly.

Clear the DTCs and turn ON the ignition with the engine OFF for 30 seconds. If a DTC P1526 sets, this indicates there is still a problem with in one of the TP circuits or with the sensors.

Use the J 35616 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.

Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems for intermittent conditions.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

The ECM performs a comparison of the signals from both throttle position sensors during the entire range of operation. If the DTC does not set with the key on and the accelerator pedal released, actuating the throttle may cause the DTC to set.

This step tests for the proper operation of the TP sensor 1 signal circuit. The ECM supplies a pull up voltage of about 4.8 volts on the signal circuit.

This step is to test the integrity of the reference ground circuit through the ECM. A small amount of current will appear on this circuit when the ECM is operational. The measured resistance of this circuit will increase when the ECM is operational. This is considered normal.

The 5-volt reference for the TP sensors and APP sensor 2 are connected inside the ECM. This step is to determine if the APP sensor is affecting the 5-volt reference circuit of the TP sensors.

The 5-volt reference for the TP sensors and APP sensor 2 are connected inside the ECM. A short to voltage on the 5-volt reference circuit of APP sensor 2 will affect the 5-volt reference circuit of the TP sensors.

The 5-volt reference for the TP sensors and APP sensor 2 are connected inside the ECM. A short to ground on the 5-volt reference circuit of APP sensor 2 will affect the 5-volt reference circuit of the TP sensors.

Additional resistance on the reference ground circuit can affect the operation of the sensors.

Additional resistance in any one of the throttle position sensor circuits can affect the operation of the sensors.

DTC P1120 Throttle Position (TP) Sensor 1 Circuit

Step

Action

Values

Yes

Schematic Reference: Engine Controls Schematics

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

Install a scan tool.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the TP sensor 1 parameter in the engine data list.

Does the scan tool indicate that the TP sensor 1 parameter is within the specified range?

0.2-4.6 V

Go to Step 3

Go to Step 5

Turn OFF the ignition for 30 seconds.
Turn ON the ignition, with the engine OFF.
With a scan tool, clear the DTC information.
Move the TP harness and the related connectors while monitoring the DTC information.

Does the harness movement cause this DTC to reset?

Go to Step 21

Go to Step 4

Continue to monitor the DTC information with the scan tool.
Slowly depress the accelerator pedal to wide open throttle (WOT) and then slowly return it to the closed position. Repeat this action several times.

Does this DTC set?

Go to Step 20

Go to Diagnostic Aids

Turn OFF the ignition.
Disconnect the TP sensor.
Turn ON the ignition, with the engine OFF.
Measure the voltage between the 5-volt reference circuit of the TP sensor and battery ground using the DMM.

Is the voltage within the specified range?

4.8-5.2 V

Go to Step 6

Go to Step 10

Measure the voltage from the TP sensor 1 signal circuit in the TP sensor harness connector to battery ground using the DMM.

Is the voltage within the specified range?

4.6-4.9 V

Go to Step 7

Go to Step 12

Important: Make sure the ECM has shut down prior to measuring the reference ground circuit resistance. This can be verified by the loss of communication on the scan tool.

Turn OFF the ignition for 30 seconds.
Measure the resistance from the reference ground circuit of TP sensor 1 to battery ground.

Is the resistance less than the specified value?

5 ohms

Go to Step 22

Go to Step 8

Disconnect the ECM connector.
Test the reference ground circuit of TP sensor 1 for an open or high resistance.
Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?