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P0450 - No power to Vapor Pressure Sensor

  #1  
Old 07-15-2017, 02:35 PM
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Post P0450 - No power to Vapor Pressure Sensor

I am constantly fighting an uphill battle with check engine codes on my 2001 Camry LX, 4 cylinder, auto. The latest is a P0450. My Haynes manual pointed to a bad Vapor Pressure Sensor, which is located on the charcoal canister behind the gas tank.

According to the manual, if I disconnect the connector and touch probes to the 2 terminals, which the key turned to the ON position, I should be reading 4.5 to 5.5 volts. I am reading nothing. No power to the VPS at all. I tested the wires an inch up from the connector and still nothing. The wires are purple and yellow.

The wiring goes up above the canister, into the area behind the back seats, then into the covered door frame. Where they come out in the engine bay I have no idea.

Does anyone have advice on this code or what to try to diagnose this lack of power? Someone on the forum once told me that there is not always power going back to the VSP, even with the key ON, but the Haynes manual says there should be power. The manual has wiring diagrams in the back, but I don't understand them very well. Any help would be greatly appreciated.
 
  #2  
Old 07-15-2017, 09:20 PM
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How many plug wires and what colors?
 
  #3  
Old 07-16-2017, 03:06 PM
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There are 2 wires going into the VSP. One is purple, the other is yellow.
 
  #4  
Old 07-17-2017, 11:24 AM
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  #5  
Old 07-28-2017, 07:15 PM
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toyomoho, sorry for the huge delay in getting back. This is the first day in weeks that I could get back to the car to work on it. After looking at the part in the link you sent, and looking again at the Haynes manual, I found out that I have been looking at the wrong part. I was looking at the "VSV for Pressure Switching Valve", located on the canister. I should have been looking at the "VAPOR PRESSURE SENSOR", located on the front of the charcoal canister on my 2001 Camry.

I put a multimeter on the Vapor Pressure Sensor connector, key on, and I did get a proper reading between 4.5 & 5 volts. The next step was to test the voltage with vacuum. I have a "Type A" VPS according to the manual, so I disconnected the larger vacuum line as instructed. A small amount of fuel came out of the hose. (Don't know it was supposed to, but that doesn't sound right to me.) I did a voltage test with back probe terminals as directed and the voltage stayed at a constant 4.1 volts. apparently that means the sensor is bad. What do you think? I wonder if the charcoal canister itself might be bad. I'm going to replace the sensor first, then move on if necessary.

Any advice?
 
  #6  
Old 07-28-2017, 09:43 PM
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Code 0440 covers canister leaks.

Are you overfilling the tank at fill ups?

Yellow and brown wires = 4.5-5 volts.
Brown is ground.
Pink is wired to yellow circuit via a resistor.

Disconnect vacuum hose to VPS. Attach vacuum pump. Ign key on check voltage between pink and brown wire. Apply (30 mmHg, 1.18 in.Hg) via pump. Voltage should be 2.9 - 3.7v for Type 1. 0.50v for Type 2.

Code set for following conditions:

10 seconds or more after engine starting condition (a) or (b) continues for 7 seconds or more:

(2 trip detection logic)
(a) vapor pressure sensor value < –4 kpa (–30 mm Hg, –1.0 in.Hg)
(b) Vapor pressure sensor value 2.1 kpa (–15 mm Hg, 0.4 in.Hg)

Possible causes:

Open or short in vapor pressure sensor circuit
Vapor pressure sensor
ECM
Fuel tank over flow check valve cracked or damaged.
 
  #7  
Old 07-29-2017, 08:26 PM
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Thanks for the quick reply. I'll use your instructions to diagnose the problem.

Also, I don't know if this is related, but I've had this car for about 5 or 6 years and it has never given me a vacuum "woosh" sound when removing the gas cap. It belonged to my father-in-law previously, and the had replaced the gas cap more than once to try to correct an engine code. I even bought a genuine Toyota filler cap and still no whoosh ever. In fact, sometimes it's a real bear trying to unscrew the cap. Could I somehow have a defective filler neck and that is somehow messing with the whole evap system? Maybe not, but it is thought I had.
 

Last edited by Whitehorse; 07-29-2017 at 08:31 PM.
  #8  
Old 08-11-2017, 09:41 AM
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I replaced the Vapor Pressure Sensor and the check engine light went out. Success, but not for long. Got another light on after about 50 miles. The new codes are: P0420, P0441 and P0446. This Camry seems to always have something going on with it. Any suggestions about these new codes?
 
  #9  
Old 08-11-2017, 03:16 PM
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Now that the vapor pressure sensor works, the system is detecting there is no or low vapor pressure.

Open or short in VSV circuit for vapor pressure sensor
VSV for vapor pressure sensor
Open or short in vapor pressure sensor circuit
Vapor pressure sensor
Open or short in VSV circuit for EVAP
VSV for EVAP
Vacuum hose cracks hole blocked damaged
Charcoal canister cracked, holed or damaged
Fuel tank over fill check valve cracked or damaged

P0420 refers to the emissions converter.
 
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