PO451 Error Code Confusion

[EddieC]

A couple weeks after having the fuel pump replaced on our '08 Tahoe the CEL came on and the stored code is P0451-00.
On first look up the text indicated "fuel tank pressure sensor performance error" but further looks noted evaporative emission (EVAP) system's pressure sensor, specifically a "range/performance" issue.
Are these referring to the same thing?
Could it related to the replacement pump or should I look elsewhere? Where?

I have not noticed any starting or running issues but probably unrelated, as noted in another thread, the fuel gage has been messed up, reading low, since the pump replacement.

 

[swathdiver]

DTC P0451
Fuel Tank Pressure (FTP) Sensor Performance

Circuit/System Description​

The fuel tank pressure (FTP) sensor measures vapor pressure or vacuum in the evaporative emission (EVAP) system. The engine control module (ECM) supplies a 5 V reference and a low reference circuit to the FTP sensor. The FTP sensor signal voltage varies depending on EVAP system pressure or vacuum. The ECM also uses this FTP signal to determine atmospheric pressure for use in the engine-off small leak test, DTC P0442. Before using this signal as an atmospheric reference it must first be re-zeroed.

Conditions for Running the DTC​

• P0451
• DTC P0451 runs only when the engine-off natural vacuum small leak test, P0442, executes.
• The number of times this test runs can range from 0–2 per engine-off period.
• The length of the test can be up to 10 min.

Conditions for Setting the DTC​

• P0451
• This DTC will set if the controller is unable to re-zero the fuel tank pressure sensor voltage within a calibrated range during the engine-off small leak test, P0442.
• The ECM must complete several engine off natural vacuum test tests before the diagnostic can turn the MIL ON or OFF.

Diagnostic Aids​

• P0451 and P0454
• A restriction in the EVAP canister or vent lines could prevent fuel vapor pressure from bleeding off fast enough. If the vent system cannot bleed off pressure fast enough, the re-zero procedure may not complete successfully, which could cause this code to set.
• Ensure that the reference port on the fuel tank pressure sensor is unobstructed.
• An fuel tank pressure sensor that is skewed or does not have a linear transition from low to high may cause this code to set. Scan tool output controls, snapshot, and plot functions can help detect erratic sensor response. To test the sensor signal under vacuum conditions, use the Quick Snapshot and the Purge/Seal functions to capture data while commanding purge to 20 %, then plot the data to look for erratic sensor operation. A similar test can be done for the pressure side of the sensor operation by applying pressure with the GE 41413-A - Evaporative Emission System Tester (EEST) while taking a snapshot.

Circuit/System Verification​

1. Remove the fuel cap.
2. Ignition ON, engine OFF.
3. Verify the scan tool Fuel Tank Pressure Sensor parameter is between 1.3 and 1.7 V.
   • If not between 1.3–1.7 V
     Refer to Circuit/System Testing
   • If between 1.3–1.7 V
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 data.
5. Verify the DTC does not set.
   • If the DTC sets
     Refer to Circuit/System Testing.
   • If the DTC does not set
6. All OK.

Circuit/System Testing​

1. Ignition OFF, all vehicle systems OFF, this may take up to 2 min, for all vehicle systems to power down. Disconnect the harness connector at the B150 Fuel Tank Pressure Sensor.
2. Test for less than 5 Ω of resistance between the low reference circuit terminal 2 and ground.
   • If 5 Ω or greater
   • Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
   • Test for less than 2 Ω in the low reference circuit end to end.
     • If 2 Ω or greater, repair the open/high resistance in the circuit.
     • If less than 2 Ω, replace the K20 Engine Control Module.
   1. If less than 5 Ω
3. Ignition ON.
4. Test for 4.8–5.2 V between the 5 V reference circuit terminal 3 and ground.
   • If less than 4.8 V
   • Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
   • Test for infinite resistance between the 5 V reference circuit and ground.
     • If less than infinite resistance, repair the short to ground on the circuit.
     • If infinite resistance
   • Test for less than 2 Ω in the 5 V reference circuit end to end.
     • If 2 Ω or greater, repair the open/high resistance in the circuit.
     • If less than 2 Ω, replace the K20 Engine Control Module.
     • If greater than 5.2 V
   • Ignition OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON.
   • Test for less than 1 V between the 5 V reference circuit and ground.
   1. If 1 V or greater, repair the short to voltage on the circuit.
   2. If less than 1 V, replace the K20 Engine Control Module.
   • If between 4.8–5.2 V
5. 5. Verify the scan tool Fuel Tank Pressure parameter is less than 0.2 V.
   • If 0.2 V or greater
   • Ignition OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON
   • Test for less than 1 V between the signal circuit terminal 1 and ground.
   1. If 1 V or greater, repair the short to voltage on the circuit.
   2. If less than 1 V, replace the K20 Engine Control Module.
   • If less than 0.2 V
6. Install a 3 A fused jumper wire between the signal circuit terminal 1 and the 5 V reference circuit terminal 3.
7. Verify the scan tool Fuel Tank Pressure Sensor parameter is greater than 4.7 V.
   • If 4.7 V or less
   • Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
   • Test for infinite resistance between the signal circuit terminal 1 and ground.
     • If less than infinite resistance, repair the short to ground on the circuit.
     • If infinite resistance
   • Test for less than 2 Ω in the signal circuit end to end.
   1. If 2 Ω or greater, repair the open/high resistance in the circuit.
   2. If less than 2 Ω, replace the K20 Engine Control Module.
   • If greater than 4.7 V
8. Test or replace the B150 Fuel Tank Pressure Sensor.

 

[EddieC]

Thanks for that.

 

[swathdiver]

Every once in a while since I've owned it, mine throws that code too. Several years ago I had a large leak in the system and replaced the charcoal canister and vent valve. It still came back but after self-tests it would pass and go away. It's an internal code on mine, doesn't trigger the CEL.

I have a new Fuel Pump assembly sitting on a shelf in the garage, the pump is still working just fine.

 

[Fless]

If you would like to see some info about what a fuel tank pressure sensor should read at atmosphere (in volts), see this link and play the video that's in post #3:

Fuel Tank Pressure Off - SOLVED

Got the P0446 code on a 2006 Tahoe so started the Evap Mystery Game. But since this truck is new to me recently and I haven't done any evap system work on it yet just decided to replace the 3 main parts that go wrong. Purge valve, Vent Valve, and the canister. Bench tested the solenoids and...

www.tahoeyukonforum.com

 

[EddieC]

Ok, it would appear that the new replacement pump installed a short time ago was faulty from the start.

Another new replacement pump with pressure sensor was installed yesterday and so far so good; fuel gage appears accurate, code has not reappeared (I know it may take time to get back in the cycle), and fuel mileage is more in line with historical values.