p0450 diagnosis

amck · Post by **amck** » 11 Dec 2017, 08:44

Hi folks, I registered to ask a question about the generic p0450 code my wife's car keeps setting, after searching around on this site and elsewhere and coming up with a dearth of information.

My questions are: will a gross leak cause this code to be set? From what I've read there is another code that I should expect to see if that's the case, so it seems that this points to LDP failure. Secondly, would low reference voltage cause this code? I got 3.8 with key on/engine off.

We bought the car 2 years ago with 106k miles; at that time the check engine light was not on, and the car seemed to be in good repair. About a year ago it threw p0133 for the o2 sensor. I traced this to a manifold leak and repaired it after much procrastination and then we took it to the dealership to have the code cleared and adaptations reset. Now, at some point when I was trying in vain to hard reset the ecm by the zip tie the battery cables together overnight method, I scanned it with my cheapo code reader and found the p0450 code... at the time I assumed this came up because I had been disconnecting the battery, but it came back a few days after having the codes cleared at the dealership.

The lines to the LDP seem intact visually, but before I went further I figured I should check voltage, ground and probe the signal with key on/engine off. Ground is good, but I'm getting a pulsing signal on the order of milliamps which seems odd. Also, the reference voltage is around 3.8v, which seems low. I have yet to inspect the purge valve. If the reference signal is a concern, then I figured I should start there. Does anyone have some insight into the evap system?

Post by **RickHaleParker** » 11 Dec 2017, 12:33

Year, model and engine?

amck · Post by **amck** » 11 Dec 2017, 12:45

2001 s40 1.9l turbo

Post by **RickHaleParker** » 13 Dec 2017, 09:13

P0450 Evaporative emission (EVAP) pressure sensor -circuit malfunction
Most probable causes: Wiring, EVAP pressure sensor, ECM

From what I gather the reference voltage from the Evap pressure sensor should be about 5V with the key off and 3 - 4.5V with the key on. Can you hook a vacuum pump to the pressure sensor and determine it to is working at all?

Did you check the fuel cap to make sure it getting a good seal? Do you have a second Volvo you can switch fuel caps with?

Leaks produce codes, P0455 Evaporative Emission Control System Leak Detected Gross Leak and P0456 EVAP Control System Leak Detected Very Small Leak.

amck · Post by **amck** » 14 Dec 2017, 07:55

Thanks Rick, it looks like the LDP is the issue. Since posting I learned a few things about how the leak detection pump differs from other evap systems. There is no pressure sensor; instead, the pump cycles until pressure in the tank is sufficient to hold the diaphragm up, closing a reed switch. The three wires I was messing with are ground, 12v and reed switch, all of which come from the ECU.

I pulled the LDP and bench tested it (found a video for how to do this on a Chrysler... In fact, the only useful info I could find on LDP was for Chrysler) on the assumption that a different code would have been set for a leak. The LDP failed; one of the valves is probably not fully closing.

With the LDP out I checked if the tank and all that would hold pressure. It does. I also checked the purge value and it's okay too. The only thing I am not totally sure of is the ecm and wiring, since I can't manually induce it to run its pressure test so I don't know for sure that it will supply 12v to the solenoid.

When I get the new LDP in I'll post here to follow up.

amck · Post by **amck** » 23 Dec 2017, 12:42

Okay, in case it may help someone out in the future, the leak detection pump was the issue. If you search youtube for "LDP bench test" you will find a helpful tutorial for chrysler; the only difference is the wiring. Also, and weirdly, the tech at the dealership told me the check valves in the vacuum system were backwards when they were not. They should be open to the manifold. Had I left them backwards, the evap system would not have been able to purge, and the LDP would not have been supplied vacuum, so it would have not only kept giving a code after it was fixed but may have developed unsafe pressure on hot days. Hm...