2014 Silverado P0451 Code - Evaporative Emission System Pressure Sensor

[Nathan Barr]

Howdy all. A few weeks ago I went to remote start my truck and it wouldn't do it. Lights would flash like it was going to and then nothing. Got in, started it without an issue and off I went. After a few days of this I disconnected the battery and let it sit. After reconnecting, no more issue.

 

Fast forward to yesterday, same thing. Finally the CEL came on. I assume this is why it's been giving me remote start fits. Plugged in my scanner and got P0451 - Evaporative emission system pressure sensor / switch range / performance.

 

Doing some reading it sounds like this is the pressure sensor on the top side of the fuel tank, is that right? I want to be sure before considering dropping the tank and replacing it.

 

As far as filling up with gas goes, on occasion the pump will shut off and I will have to start it again but it's probably 1/10th of the time when filling up.

 

EVAP_VP (inH2O) shows -3.0 - -4.9 if that matters.

 

Thanks all!

2014 Silverado LT

4x4 5.3L

99k miles

Edited January 23, 2024 by Nathan Barr

[Snowcamo]

The sensor on top of the tank can be replaced without removing the gas tank.  Not hard,  but easier if you look at it with an inspection mirror.  

 

All that said.  This is a code I and others have chased.  I replaced that sensor worked for a little while.  Idk if anyone has found a resolve for this issue.  I feel like it is a gasket in the hose leading from the emissions eq. By the tank to the engine. 

[Nathan Barr]

1 hour ago, Snowcamo said:

The sensor on top of the tank can be replaced without removing the gas tank.  Not hard,  but easier if you look at it with an inspection mirror.  

 

All that said.  This is a code I and others have chased.  I replaced that sensor worked for a little while.  Idk if anyone has found a resolve for this issue.  I feel like it is a gasket in the hose leading from the emissions eq. By the tank to the engine. 

 

I was looking up some videos and found a couple of different ways to get to it. One involved lifting one side of the bed, the other removed the drive shaft, etc. Do you know what the best method is? I will try to just look today and see if I can't find an easy access way to it...

[Snowcamo]

Yeah removing the driveshaft would make it easier. I just sat under the truck and reached over it. 

 

You can see it between the bed and cab or bed and frame. 

[Nathan Barr]

6 minutes ago, Snowcamo said:

Yeah removing the driveshaft would make it easier. I just sat under the truck and reached over it. 

 

You can see it between the bed and cab or bed and frame. 

Love to hear that. I'll take a gander today and see what I can see.

 

I just wanted to make sure it wasn't something under the hood. Videos seem split. Some point to the EVAP stuff there but I was pretty positive it didn't have to do with that.

[Snowcamo]

Well like I was saying earlier, I don't think anyone has come up with a fix. I do suspect it to be a hose leak though. I have changed that sensor and evap stuff by the tank. Still the light persist. Over 4years no issues due to that light/ code.

 

I've even asked gm techs and they have no clue. 

[asilverblazer]

The fuel tank pressure 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 fuel tank pressure sensor. The fuel tank pressure sensor signal voltage varies depending on EVAP system pressure or vacuum. The control module also uses this fuel tank pressure 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.

P0452 and P0453

DTC P0452 and P0453 run continuously when the ignition is ON.

P0454

• DTC P0454 runs only when the engine-off natural vacuum small leak test, P0442, executes.
• This test can run once per engine-off period. The length of the test can be up to 10 min.
• A refueling event is not detected. A refueling event is confirmed if the fuel level has a persistent change of 10% for 30 s during a 10 min refueling rationality test.

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.

P0452

The fuel tank pressure sensor voltage is less than 0.15 V for greater than 10 s.

P0453

The fuel tank pressure sensor voltage is more than 4.85 V for greater than 10 s.

P0454

• If, during the engine-off natural vacuum small leak test, P0442, the ECM detects an abrupt fuel tank pressure signal change, other than a refueling event, this DTC will set. An abrupt change is defined as a change of greater than 0.45 in H2O in the span of 1 s but less than 1 in H2O in 12.5 ms.
• This test must fail twice in three samples to set this DTC.

Action Taken When the DTC Sets

• DTCs P0451 and P0454 are Type A DTCs.
• DTCs P0452 and P0453 are Type B DTCs.

Conditions for Clearing the MIL/DTC

• DTCs P0451 and P0454 are Type A DTCs.
• DTCs P0452 and P0453 are Type B DTCs.

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 DTC to set. Scan tool Control Functions, 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 while taking a snapshot.

[Nathan Barr]

18 hours ago, asilverblazer said:

The fuel tank pressure 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 fuel tank pressure sensor. The fuel tank pressure sensor signal voltage varies depending on EVAP system pressure or vacuum. The control module also uses this fuel tank pressure 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.

P0452 and P0453

DTC P0452 and P0453 run continuously when the ignition is ON.

P0454

• DTC P0454 runs only when the engine-off natural vacuum small leak test, P0442, executes.
• This test can run once per engine-off period. The length of the test can be up to 10 min.
• A refueling event is not detected. A refueling event is confirmed if the fuel level has a persistent change of 10% for 30 s during a 10 min refueling rationality test.

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.

P0452

The fuel tank pressure sensor voltage is less than 0.15 V for greater than 10 s.

P0453

The fuel tank pressure sensor voltage is more than 4.85 V for greater than 10 s.

P0454

• If, during the engine-off natural vacuum small leak test, P0442, the ECM detects an abrupt fuel tank pressure signal change, other than a refueling event, this DTC will set. An abrupt change is defined as a change of greater than 0.45 in H2O in the span of 1 s but less than 1 in H2O in 12.5 ms.
• This test must fail twice in three samples to set this DTC.

Action Taken When the DTC Sets

• DTCs P0451 and P0454 are Type A DTCs.
• DTCs P0452 and P0453 are Type B DTCs.

Conditions for Clearing the MIL/DTC

• DTCs P0451 and P0454 are Type A DTCs.
• DTCs P0452 and P0453 are Type B DTCs.

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 DTC to set. Scan tool Control Functions, 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 while taking a snapshot.

 

Thank you for that. My simple little scan tool isn't that fancy so the only "test" I was able to do was to monitor the inH2O while revving to 3k RPM's and holding it. In doing this, that number went from about -2.9 to -5.0. After letting off of the throttle, it backed down to around -2.9.

 

I'm not entirely sure if that means anything at all or if I should just look at replacing the sensor on the fuel tank.

[asilverblazer]

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
    
   1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
   2. 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.
      
      
       
    
   • 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
    
   1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
   2. 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
      
      
   3. 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
    
   1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON.
   2. Test for less than 1 V between the 5 V reference circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the K20 Engine Control Module.
      
      
       
    
   • If between 4.8–5.2 V
   
   
5. Verify the scan tool Fuel Tank Pressure parameter is less than 0.2 V.
   • If 0.2 V or greater
    
   1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON
   2. Test for less than 1 V between the signal circuit terminal 1 and ground.
    
   • If 1 V or greater, repair the short to voltage on the circuit.
   • 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
    
   1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
   2. 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
      
      
   3. Test for less than 2 Ω in the signal 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 4.7 V
   
   
8. Test or replace the B150 Fuel Tank Pressure Sensor.

[asilverblazer]

Looks like all that boiled down is check the wiring then either ECM (not likely) or the sensor... in addition to:

 

21 hours ago, asilverblazer said:

• 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 DTC to set. Scan tool Control Functions, 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 while taking a snapshot.

 

[Snowcamo]

1 minute ago, asilverblazer said:

Looks like all that boiled down is check the wiring then either ECM (not likely) or the sensor... in addition to:

 

 

Ok let's say I wanted to replace that sensor wire.  Where does the other end terminate? 

[asilverblazer]

gmupfitter has wiring diagrams to view...

 

However, I would focus on the connections and look for other obvious wire/harness damage first. A random broken wire is much less common to require a replacement of it. 

 

The code (P0451) is very specific to not being able to determine a correct 'zero' value and suggests that other elements may be preventing that (crimped or obstructed hose). 

 

Since your scan tool isn't able to properly test for those faults, the above post would be the next step (we are assuming there is no fault vs. testing and confirming there is none) and checking the electrical circuit.

 

Because proper tests haven't confirmed all else to be OK, I wouldn't spend a significant effort to chase down a potential electrical circuit failure that isn't very likely. Unplug it and look at it... see what you think. maybe clean the pins connection. Perhaps just some basic checks, disconnect the sensor and verify the appropriate voltage/resistance per the post above at the connector pins. If a deficiency is found, probe the backside of the connector/wire. The likeliest electrical failure points I think would be the connection to the sensor or the sensor itself.

 

Narrowing down the 'likeliest faults':

1. Obstruction or other condition preventing the sensor from getting an accurate reading. 

2. Sensor electrical connection.

3. Sensor failure.

 

Based on that, I would buy a new sensor, crawl under the truck with the intention of replacing it and doing so unless I found an obvious problem with item 1 and/or 2. 

 

If the problem remains, then I would start chasing that circuit in more depth. Keeping in mind that testing for obstructions in the EVAP canister or vent lines hasn't been fully completed.

[Nathan Barr]

17 minutes ago, asilverblazer said:

gmupfitter has wiring diagrams to view...

 

However, I would focus on the connections and look for other obvious wire/harness damage first. A random broken wire is much less common to require a replacement of it. 

 

The code (P0451) is very specific to not being able to determine a correct 'zero' value and suggests that other elements may be preventing that (crimped or obstructed hose). 

 

Since your scan tool isn't able to properly test for those faults, the above post would be the next step (we are assuming there is no fault vs. testing and confirming there is none) and checking the electrical circuit.

 

Because proper tests haven't confirmed all else to be OK, I wouldn't spend a significant effort to chase down a potential electrical circuit failure that isn't very likely. Unplug it and look at it... see what you think. maybe clean the pins connection. Perhaps just some basic checks, disconnect the sensor and verify the appropriate voltage/resistance per the post above at the connector pins. If a deficiency is found, probe the backside of the connector/wire. The likeliest electrical failure points I think would be the connection to the sensor or the sensor itself.

 

Narrowing down the 'likeliest faults':

1. Obstruction or other condition preventing the sensor from getting an accurate reading. 

2. Sensor electrical connection.

3. Sensor failure.

 

Based on that, I would buy a new sensor, crawl under the truck with the intention of replacing it and doing so unless I found an obvious problem with item 1 and/or 2. 

 

If the problem remains, then I would start chasing that circuit in more depth. Keeping in mind that testing for obstructions in the EVAP canister or vent lines hasn't been fully completed.

 

So replacing the sensor would come before looking at replacing the canister under the hood, correct?

[asilverblazer]

1 hour ago, Nathan Barr said:

 

So replacing the sensor would come before looking at replacing the canister under the hood, correct?

Based on code P0451, that is how I would proceed.

[Nathan Barr]

22 minutes ago, asilverblazer said:

Based on code P0451, that is how I would proceed.

Thank you! I disconnected the battery yesterday to clear things out and see if it comes back. Time will tell but I have a feeling I will be replacing or in the least diagnosing that sensor.