GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2004 🢒 SRX 🢒 Engine 🢒 Engine Controls - 4.6L (LH2) 🢒 DTC P0451

Circuit Description

The fuel tank pressure (FTP) sensor measures the difference between the air pressure or vacuum in the evaporative emission (EVAP) system and the outside air pressure. The control module supplies a 5-volt reference and a low reference circuit to the FTP sensor. The FTP sensor signal circuit voltage varies depending on EVAP system pressure or vacuum. If the FTP sensor signal voltage becomes fixed while driving, or fluctuates more than a calibrated amount at idle, this DTC sets.

The following table illustrates the relationship between the FTP sensor signal voltage and the EVAP system pressure/vacuum.

FTP Sensor Signal Voltage

Fuel Tank Pressure

High, Approximately 1.5 Volts or More

Negative Pressure/Vacuum

Low, Approximately 1.5 Volts or Less

Positive Pressure

Conditions for Running the DTC
    • DTCs P0030, P0031, P0032, P0036, P0037, P0038, P0050, P0051, P0052, P0056, P0057, P0058, P0068, P0101, P0102, P0103, P0111, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0139, P0140, P0141, P0150, P0151, P0152, P0153, P0154, P0155, P0156, P0157, P0158, P0159, P0160, P0161, P0201, P0202, P0203, P0204, P0205, P0206, P0221, P0222, P0223, P0308, P0313, P0443, P0446, P0449, P0452, P0453, P0454, P0458, P0459, P0496, P0498, P0499, P0506, P0507, P1271, P1277, P1278, P1282, P1283, P1511, P1516, P1519, P1523, P1526, P1530, P1551, P2107, P2100, P2101, P2119, P2122, P2123, P2127, P2128, 2138, P2176 are not set.
    • The engine is idling.
    • The FTP has varied at least once before idling.
        OR
    • The vehicle speed is more than 45 km/h (28 mph).
    • The canister is purging.
    • The FTP is more than 0.02 volts.

Conditions for Setting the DTC
    • The FTP varies more than 0.37 mmHg (0.2 inches H2O) for 5 seconds at idle.
        OR
    • The FTP varies less than 0.02 volts for 5 seconds while driving.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the 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.

Step

Action

Value(s)

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2
  1. Idle the engine for 1 minute.
  2. Monitor the DTC information using the scan tool.

Did DTC P0651 fail this ignition?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3
  1. Turn ON the ignition, with the engine OFF.
  2. Disconnect the fuel tank pressure (FTP) sensor.
  3. Measure the voltage from the 5-volt reference circuit of the FTP sensor to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the voltage within the specified value?

4.9-5.1 V

Go to Step 4

Go to Step 6

4
  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the FTP sensor and the signal circuit of the FTP sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the FTP sensor voltage with a scan tool.

Is the Fuel Tank Pressure sensor parameter within the specified value?

4.9-5.1 V

Go to Step 5

Go to Step 8

5

Measure the voltage from the 5-volt reference circuit to the low reference circuit with a DMM.

Is the voltage within the specified value?

4.9-5.1 V

Go to Step 9

Go to Step 7

6

Test the 5-volt reference circuit for an open circuit or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

7

Test the low reference circuit of the FTP sensor for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

8

Test the signal circuit for the following conditions:

    • High resistance
    • Damage
    • Corrosion

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

9

Test for an intermittent and for a poor connection at the FTP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 11

10

Test for an intermittent and for a poor connection at the control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

11

Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement .

Did you complete the replacement?

--

Go to Step 13

--

12

Replace the control module. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 13

--

13

Important: DO NOT exceed the specified value in this step. Exceeding this specified value may produce incorrect test results.

  1. Connect the J 41413-200 Evaporative Emissions System Tester (EEST) to the fuel fill pipe.
  2. Turn the nitrogen/smoke valve to NITROGEN.
  3. Seal the EVAP Purge/Seal function with a scan tool.
  4. Pressurize the EVAP system to the specified value.
  5. Observe the fuel tank pressure sensor parameter with a scan tool.

Does the fuel tank pressure sensor parameter remain constant?

5 in H2O

Go to Step 14

Go to Step 2

14

Observe the fuel tank pressure sensor parameter with a scan tool.

Is the difference between the scan tool fuel tank pressure sensor parameter and the J 41413-200 gage within the specified value?

1 in H2O

Go to Step 15

Go to Step 2

15
  1. Observe the fuel tank pressure parameter with the engine OFF.
  2. Increase the EVAP purge solenoid valve to 100 percent.

Does the pressure decrease?

--

Go to Step 16

Go to Step 2

16
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 17

17

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK