1998 chevy cavalier 2.2 lit. standard. dtc states that the evap pressure sensor that sits on top of the fuel pump showing low voltage. after erasing the code, the ck eng lite comes back on, but no code. could the computer be bad. please advise. thanks in advance.

DTC P0452 Fuel Tank Pressure Sensor Circuit Low Voltage

The fuel tank pressure sensor is located on top of the fuel tank.

Circuit Description
The fuel tank pressure sensor measures the pressure (or vacuum) in the fuel tank. The powertrain control module (PCM) provides the sensor with a reference voltage, a signal circuit, and a ground. The sensor returns a signal voltage to the PCM relative to the pressure in the fuel tank. The PCM should see a signal voltage increase as the pressure in the tank decreases (more vacuum). As the pressure in the tank increases (less vacuum), the PCM should see a signal voltage decrease. The PCM uses the sensor signal to test the integrity of the EVAP system. If the PCM detects a signal voltage that is too low, DTC P0452 will set.


Your best bet , take your vehicle to a qualified repair shop.

Good explanation of the problem and suggestions at the link below.

https://www.obd-codes.com/p0452

Your fuel pressure is really low.

Electronic throttle control !
DTC P2120: Accelerator Pedal Position (APP) Sensor 1 Circuit
DTC P2122: Accelerator Pedal Position (APP) Sensor 1 Circuit Low Voltage
DTC P2123: Accelerator Pedal Position (APP) Sensor 1 Circuit High Voltage
DTC P2125: Accelerator Pedal Position (APP) Sensor 2 Circuit
DTC P2127: Accelerator Pedal Position (APP) Sensor 2 Circuit Low Voltage
DTC P2128: Accelerator Pedal Position (APP) Sensor 2 Circuit High Voltage
DTC P2138: Accelerator Pedal Position (APP) Sensor 1-2 Correlation

2009 Chevy Silverado P2138 Accelerator Pedal Position


Circuit/System Description
The throttle actuator control (TAC) system uses two accelerator pedal position (APP) sensors to monitor the accelerator pedal position. The APP sensors 1 and 2 are located within the pedal assembly. Each sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit.
Two processors are also used to monitor the TAC system data. Both processors are located within the engine control module (ECM). Each signal circuit provides both processors with a signal voltage proportional to pedal movement. The processors share and monitor data to verify that the indicated APP calculation is correct.

DTC P0455: Evaporative Emission (EVAP) System Large Leak

The control module tests the evaporative emission (EVAP) system for a large leak. The control module monitors the fuel tank pressure (FTP) sensor signal to determine the EVAP system vacuum level. When the conditions for running are met, the control module commands the EVAP canister purge solenoid valve OPEN and the EVAP vent solenoid valve CLOSED. This allows engine vacuum to enter the EVAP system. At a calibrated time, or vacuum level, the control module commands the EVAP canister purge solenoid valve closed, sealing the system, and monitors the FTP sensor input in order to determine the EVAP system vacuum level. The following table illustrates the relationship between the ON and OFF states, and the OPEN or CLOSED states of the EVAP canister purge and vent solenoid valves.

What light stay's on ? GM had stepper motor problems 2003 to 2006 . stepper motor in side instrument cluster is what controls the gauge needle . Video's on youtube GM stepper motor problems . Do you know what evaporative emissions systems are ?
DTC P0449 Evaporative Emission (EVAP) vent Solenoid Control Circuit
A battery positive voltage is supplied to the evaporative emission (EVAP) canister vent solenoid valve. The control module grounds the EVAP canister vent solenoid valve control circuit to close the valve by means of an internal switch called a driver. The scan tool displays the commanded state of the EVAP canister vent solenoid valve as ON or OFF. The control module monitors the status of the driver. If the control module detects an incorrect voltage for the commanded state of the driver, this DTC sets.

DTC P0463 Fuel Level Sensor 1 Circuit High Voltage
The fuel level sensor changes resistance in response to fuel level. The powertrain control module (PCM) monitors the signal circuit of the fuel level sensor in order to determine the fuel level. When the fuel tank is full, the sensor resistance is low and the PCM senses a low signal voltage. When the fuel tank is empty, the sensor resistance is high and the PCM senses a high signal voltage. The PCM uses the signal circuit of the fuel level sensor in order to calculate the percentage of remaining fuel in the tank. The PCM sends the fuel level percentage via the class 2 serial data circuit to the instrument cluster in order to control the fuel gage. The fuel level information is also used for misfire and evaporative emission (EVAP) diagnostics.
With this code stored would suspect sending unit in the fuel tank or a wiring problem . Your best bet mite be to have a qualified repair shop check it out .

Fuel Pump Flow Control Module (FPCM) - LMF
The fuel pump flow control module (FPCM) is a serviceable GMLAN module. The FPCM receives the desired fuel pressure message from the engine control module (ECM) and controls the fuel pump located within the fuel tank to achieve the desired fuel pressure. The FPCM sends a 25 KHZ PWM signal to the fuel pump, and pump speed is changed by varying the duty cycle of this signal. Maximum current supplied to the fuel pump is 15 amps. A liquid fuel pressure sensor provides fuel pressure feedback to the FPCM.
Electronic Returnless Fuel System (ERFS) - LMF
The electronic returnless fuel system is a microprocessor controlled fuel delivery system which transports fuel from the tank to the fuel rails. It functions as an electronic replacement for a traditional, mechanical fuel pressure regulator. A pressure vent valve within the fuel tank provides an added measure of fuel pump flow control module (FPCM). Desired fuel pressure is commanded by the engine control module (ECM), and transmitted to the FPCM via a GMLAN serial data message. A liquid fuel pressure sensor provides the feedback the FPCM requires for Closed Loop fuel pressure control.

Fuel Pump Flow Control Module (Gas except LU3/LMG/LY6/LC9)
Mounted to the rear frame, near the spare tire mount
Wheels/Vehicle Underbody Component Views
Component Connector End Views
Fuel Pump Relay - Secondary (Gas with LY6)
On the fuse block - underhood bracket

DTC P0191: Fuel Rail Pressure (FRP) Sensor Performance
DTC P0192: Fuel Rail Pressure (FRP) Sensor Circuit Low Voltage
DTC P0193: Fuel Rail Pressure (FRP) Sensor Circuit High Voltage
DTC P0230: Fuel Pump Relay Control Circuit
The engine control module (ECM) sends the fuel enable signal to the fuel pump control module (FPCM). The control module monitors the voltage on the fuel pump relay control circuit. If the control module detects an incorrect voltage on the fuel pump relay control circuit, a fuel pump relay control DTC sets.
The control module monitors the voltage on the fuel pump relay control circuit. If the control module detects an incorrect voltage on the fuel pump relay control circuit, a fuel pump relay control DTC sets.
DTC P0231: Fuel Pump Control Circuit Low Voltage
DTC P0232: Fuel Pump Control Circuit High Voltage
DTC P023F: Fuel Pump Control Circuit
DTC P025A: Fuel Pump Control Module Enable Circuit

Your best bet , take it to a qualified repair shop , dealer .

Ran a hot wire to what fuel pump or the control module ? Which of these is yours ?
Figure 9: Fuel Controls - Fuel Pump Controls (LY6)
Figure 10: Fuel Pump Flow Control Module (Except LY6) Does yours have fuel pump flow control module under the vehicle Fuel Pump Flow Control Module (except LY6)
Mounted to the left side of the frame assembly below the driver seat ?
Fuel Pump Flow Control Module (FPCM) - LMF
The fuel pump flow control module (FPCM) is a serviceable GMLAN module. The FPCM receives the desired fuel pressure message from the engine control module (ECM) and controls the fuel pump located within the fuel tank to achieve the desired fuel pressure. The FPCM sends a 25 KHZ PWM signal to the fuel pump, and pump speed is changed by varying the duty cycle of this signal. Maximum current supplied to the fuel pump is 15 amps. A liquid fuel pressure sensor provides fuel pressure feedback to the FPCM.
Electronic Returnless Fuel System (ERFS) - LMF
The electronic returnless fuel system is a microprocessor controlled fuel delivery system which transports fuel from the tank to the fuel rails. It functions as an electronic replacement for a traditional, mechanical fuel pressure regulator. A pressure vent valve within the fuel tank provides an added measure of fuel pump flow control module (FPCM). Desired fuel pressure is commanded by the engine control module (ECM), and transmitted to the FPCM via a GMLAN serial data message. A liquid fuel pressure sensor provides the feedback the FPCM requires for Closed Loop fuel pressure control.
If your vehicle has this system check it for DTC'S - diagnostic trouble codes . Will take guess work out of it .
DTC P0191: Fuel Rail Pressure (FRP) Sensor Performance
DTC P0192: Fuel Rail Pressure (FRP) Sensor Circuit Low Voltage
DTC P0193: Fuel Rail Pressure (FRP) Sensor Circuit High Voltage
DTC P0230: Fuel Pump Relay Control Circuit
DTC P0231: Fuel Pump Control Circuit Low Voltage
DTC P0232: Fuel Pump Control Circuit High Voltage
DTC P023F: Fuel Pump Control Circuit
The engine control module (ECM) supplies voltage to the fuel pump flow control module (FPCM) when the ECM detects that the ignition is on. The voltage from the ECM to the FPCM remains active for 2 seconds, unless the engine is in crank or run. While this voltage is being received, the FPCM supplies a varying voltage to the fuel tank pump module in order to maintain the desired fuel rail pressure.
DTC P025A: Fuel Pump Control Module Enable Circuit .
Ford Electronic Returnless Fuel System Diagnosis Part 1 this for ford but the GM system works the same . You'll need a wiring diagram so you know what wires are what . Free wiring diagrams http://www.bbbind.com/free_tsb.html

DTC P0452 - FTP (Fuel Tank Pressure) sensor circuit low voltage
The Powertrain Control Module (PCM) monitors the Fuel Tank Pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the enhanced Evaporative Emission (EVAP) diagnostic. The PCM supplies a 5-volt reference and ground to the sensor. The FTP sensor signal voltage increases when the fuel tank pressure decreases. Negative pressure or vacuum indicates high voltage. The FTP sensor signal voltage decreases when the fuel tank pressure increases. Positive pressure indicates low voltage. This DTC sets when the FTP sensor signal goes below a predetermined value.

Circuit Description
The Fuel Tank Pressure Sensor responds to changes in the fuel tank pressure or vacuum. This information is used in order to detect vacuum decay or an excessive vacuum during the EVAP diagnostic routing. The fuel tank pressure sensor signal voltage to the VCM varies from a minimum of about 0.1 volts with pressure in the fuel tank to above 4.0 volts with a high vacuum in the fuel tank.

The Fuel Tank Pressure sensor display on the scan tool has an auto zero feature which occurs at each ignition cycle and is corrected according to the barometric pressure. Because of this, the Fuel Tank Pressure sensor display may not accurately reflect the actual output of the sensor or the conditions within the fuel tank.

The Fuel Tank Pressure Sensor diagnosis table is intended to isolate and diagnose the electrical problems with the sensor wiring or the sensor.

Conditions for Running the DTC
The ignition switch is in the RUN position.

Conditions for Setting the DTC
The fuel tank pressure sensor voltage is less than 0.1 volt for more than 5 seconds.

Action Taken When the DTC Sets
The VCM turns ON the MIL after 2 consecutive driving cycles with the fault active.

Conditions for Clearing the MIL/DTC
* The Control Module turns OFF the MIL after X trips when the test has Run and Passed.
* A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the Engine Coolant Temperature is more than 70°C (158°F) during the same ignition cycle).
* Use the scan tool Clear Information function.

Diagnostic Aids
1. Inspect the Control Module harness connectors for the following conditions:
* Improper mating
* Broken locks
* Improperly formed
* Damaged terminals

2. Inspect the wiring harness for damage. If the harness appears to be OK, observe the Fuel Tank Pressure sensor display on the scan tool while moving the connectors and the wiring harnesses related to the sensor. A change in the display will indicate the location of the fault.

Test Description
The number(s) below refer to the step number(s) on the diagnostic table.



If the VCM recognizes the high signal voltage, the VCM and the wiring are fine.

Good luck.

DTC P0446 - Evaporative Emmission Control System Vent Control Circuit
Evap vent valve has only one purpose. It closes in order to seal the vent so the EVAP system can pressurize and ensure there are no leaks. Evap vent valve is usually supplied Batt. voltage with key on. The ECM's driver controls the ground, and when grounded, activates the valve (closing it). If the ECM detects a short to ground, and open,or a short to battery voltage on the control circuit, P0446 will set. Code also may refer to ECM detecting that EVAP system is unable to achieve or maintain vacuum during test. A code P0446 could mean one or more of the following has happened:

• Faulty vent valve
• Open, short or excessive resistance on Vent valve control circuit
• Blockage of vent valve
• Bad PCM

Possible Solutions

• Replace Vent valve
• Repair open, short, or resistance problem in control circuit
• Repair open, or short, or resistance problem in power circuit
• Replace PCM

DTC P0452 - Evaporative emission control system, pressure sensor low imput
DTC P0453 - Evaporative emission control system, pressure sensor high imput

The PCM monitors the EVAP control system FTP sensor input signal to the PCM. The test fails when the signal average jumps above a minimum allowable calibrated parameter. If both codes are present, it sounds like your fuel tank pressure sensor has failed.

The sensor is on top of the tank and you will have to remove the tank. But your symptoms are pointing to more than just the sensor. You may have wiring problems.


Hope this helps (remember to rate and leave a comment about this free answer).

DTC 1491 (VACUUM CUT VALVE BYPASS VALVE) DIAGNOSIS

SERVICE PROCEDURE

1. Confirm the Vacuum Cut Valve is installed correctly

NOTE :

^ The Vacuum Cut Valve will not work correctly and a DTC will be stored if it is installed upside-down.

^ The Vacuum Cut Valve is a white plastic valve near the fuel tank and EVAP canister.


2. Connect CONSULT-II and turn the ignition key to "N" (do not start the engine).

3. On CONSULT II, select ENGINE - DATA MONITOR - SELECTION FROM MENU - EVAP SYSTEM PRESSURE SENSOR.

4. Note the EVAP System Pressure Sensor Voltage Confirm that it is reading in a normal range for a key ON arid engine OFF condition.

NOTE :For 2001 models and earlier:

^ Voltage in step 4 should be near 3.36 volts.

^ The normal range is between 3.32 - 3.40 volts.


For 2002 models:

^ Some 2002 models use a new type EVAP System Pressure Sensor with different operational characteristics.

^ Refer to the EC section of the appropriate Service Manual to determine which type sensor your vehicle is equipped with.

^ Models that use the new type EVAP System Pressure Sensor will have a voltage reading that varies with changes in the "barometric" pressure (atmospheric air pressure that changes with altitude and/or weather conditions).

^ The usual voltage range obtained in step 4 with the new type EVAP System Pressure Sensor is between 3.8 and 4.2 volts. Because this range will vary with barometric pressure, it is best to compare readings with a known good vehicle.

^ Some 2002 models use the earlier type EVAP System Pressure Sensor (same as used on 2001 and earlier models). The normal range for the earlier type is 3.32 to 3.40 volts and does not vary with barometric pressure.


5. Start the engine. Observe the EVAP System Pressure Sensor voltage.

^ If the value has reduced 0.04 volts or more from the reading obtained in step 4, the EVAP Canister Purge Volume Control Solenoid Valve may be leaking.

^ Refer to the EC section of the appropriate Service Manual for inspection procedures of the EVAP Canister Purge Volume Control Solenoid Valve, DTC P1444.


NOTE :The EVAP Canister Purge Volume Control Solenoid Valve is located in the engine compartment.

6. Perform the DTC Confirmation Procedure for DTC P1491. Refer to the EC section of the appropriate Service Manual for confirmation procedure steps and driving conditions.

7. If the DTC confirmation results are NG, do the following:

a. Refer to the EC section of the appropriate Service Manual to determine if the vehicle is equipped with On-Board Refueling Vapor Recovery (ORVR).

^ If the vehicle has ORVR, go to b.

^ If the vehicle does NOT have ORVR, go to step 8.

b. Place a clamp on the Refueling EVAP Vapor Line near the fuel tank. The Refueling EVAP Vapor Line is the larger hose (see figure 2). Use hose clamp (3M P/N # 08556-1), found in Fuel Injector Cleaning Kit J-45701, or equivalent.

c. Retry DTC Confirmation Procedure

d. If the result is now OK, the Refueling Control Valve may be leaking and should be inspected. Refer to the EC section of the appropriate Service Manual for Refueling Control Valve inspection procedures.

8. If the DTC confirmation is still NG after step 7, or the vehicle is not equipped with ORVR, do the following:

a. Disconnect two (2) lines from the Vacuum Cut Valve. One that goes to the fuel tank and one that goes to the EVAP Canister (see figure 1).

b. Use a hand vacuum pump to check each of the two (2) disconnected hoses for free flow. Make sure they are clear into the fuel tank (vent line) and into the EVAP Canister (see figure 2).


NOTE :

^ Figure 2 includes ORVR system. Refer to the appropriate service manual to determine if your vehicle has ORVR or not.

^ The lines between the Vacuum Cut Valve and Fuel Tank, and between the Vacuum Cut Valve and EVAP Canister may go through a metal line. Make sure the lines are clear between the Vacuum Cut Valve and Fuel Tank, and between the Vacuum Cut Valve and EVAP Canister, including any metal lines.

c. If any blockage is found, determine the cause and repair as necessary. Blockage in either of these lines will cause a DTC.


9. If all of the above checks do not locate the source of the incident, refer to the appropriate Service Manual for further DTC P1491 diagnosis.