OT: Any auto savvy guys? (MAP sensor question)

[TronnyJenkins]

Guys, I'm trying to get my inspection to pass and with all the smog restrictions in effect here in DFW, I need my check engine light to go off. I replaced my knock sensors yesterday (what a job!) and the SES light came back on today, so I feared I was going to have to take the manifold off again. Yikes! Luckily I went to AutoZone today and the code was actually 'low input' on the MAP (Manifold Air Pressure) sensor. Popped the hood, and it looks like I inadvertently pulled out an air hose as I was maneuvering the manifold back into place. Hose is now reinstalled, but how long might it take for the light to go off? Should I just reset the computer and drive the 50 miles to get all the sensors ready?

2001 GMC Yukon, 2WD, 5.3 V8.

[zmudshark]

I cant speak as to the Yukon, but one of my cars (2005 Miata) has a very specific driving sequence to reset the OBD to pass emissions. Just driving 50 miles doesn't do it.

[Hilltopperny]

I'd try to reset the sensor and drive the 50 miles first. That should take care of it as long as that was the only issue:beer:

[buldogge]

Yes...You need to clear the codes, and then run it for some miles. There are various readiness tests, and they require different time/distances.

Clear, drive...test the next day. (or get a reader and check readiness)

-Mark in St. Louis

Guys, I'm trying to get my inspection to pass and with all the smog restrictions in effect here in DFW, I need my check engine light to go off. I replaced my knock sensors yesterday (what a job!) and the SES light came back on today, so I feared I was going to have to take the manifold off again. Yikes! Luckily I went to AutoZone today and the code was actually 'low input' on the MAP (Manifold Air Pressure) sensor. Popped the hood, and it looks like I inadvertently pulled out an air hose as I was maneuvering the manifold back into place. Hose is now reinstalled, but how long might it take for the light to go off? Should I just reset the computer and drive the 50 miles to get all the sensors ready?

2001 GMC Yukon, 2WD, 5.3 V8.

[sand fungus]

I think there may also be a number of ignition cycles that have to pass before the code will clear. Assuming that you checked and the code is not active.

[TronnyJenkins]

Cool. Hopefully it does not have the sequence of the 2005 Miata, haha!
I need to get this all sorted by next Friday because I already paid for my state inspection and quickly am running out of days to take it by the inspector with no codes.

[PeregrineA1]

Disconnect the battery for a few minutes, reconnect and drive. Works for some things on a Ford circa 1997.

[Tony T]

Couldn't AutoZone clear the code/light with their reader?

edit: As Peregrine said, disconnect the battery for a few minutes.

[cmbicycles]

Auto zone should be able to clear the code, unless they have a policy to not do so. Most except the really cheap reader-only scanners will clear the code.

[kramnnim]

Buy a scanner from Walmart if Autozone won't do it. Then do this- http://www.obdii.com/DRIVECYCLE.HTML and rescan.

[TronnyJenkins]

I think AutoZone isn't supposed to, at least what they told me.
Thanks for the drive cycle guide.

[GregL]

Buy a scanner from Walmart if Autozone won't do it. Then do this- http://www.obdii.com/DRIVECYCLE.HTML and rescan.
+1 on checking the OBD-II drive cycle. Knowing the exact drive cycle your vehicle requires can save you lots of wasted driving. Some of the cycles are nearly impossible to meet in everyday driving.

Greg

[zmudshark]

Buy a scanner from Walmart if Autozone won't do it. Then do this- http://www.obdii.com/DRIVECYCLE.HTML and rescan.That's close to what my Mazda requires.

[carpediemracing]

If there is a code then you won't pass a normal emissions inspection. OBD has three basic states:
1. INC (incomplete, has not done its self test cycles)
2. OK (has done its test cycles, passed itself)
3. ON? (has done its test cycles, failed itself).

I forget the exact terms, but INC and OK are in there. If the check engine light is on you'll have a MIL status of ON, and at that point most places will fail you. CT will for sure, for example.

The place where I work does not reset codes. One reason is that it's a red herring. Resetting a code doesn't fix the problem but a LOT of people think that they should pass emissions if we clear a code, and they get very upset when they don't. Clearing the code forces the car to do another self test cycle, which, as pointed out, is a bit involved. I know that idling for a few minutes with the engine under load (AC and defrost on) is one thing that gets tested, another is slowing by coasting from 50 mph or so (as if coming up on a red light but with zero or light brake use). There are other cycles but not sure what they are.

Another reason for not resetting a code is that the car may be for sale and the owner is clearing the code temporarily to rip off a potential customer. I turned away one guy who was belligerent and swearing and yelling at all the other customers how we ripped him off because we wouldn't do a simple code reset and that "everyone else does it".

So generally speaking a big business will never clear a code unless they did work meant to address the code ("We'll clear the code only if you pay us to fix what's causing the code" "So you won't clear the code unless I pay you thousands of dollars to fix my car first? You're a bunch of thieving rip off con artists!"). A small garage might do it but clearing the code won't do you any good because there is no "self test results" left.

You can buy a scanner for $20 or so on Amazon to clear the code yourself.

In my example, off my car, there's an incomplete (INC), an OK, and a N/A (not applicable, i.e. the car doesn't have it).

https://1.bp.blogspot.com/-eNzueFLLMPs/WJXk6Q5EGbI/AAAAAAAAJgE/afdgA3dfdw4EAV7ZaEhB4flNg6qvBUbkwCLcB/s800/1210160946c.jpg

[TronnyJenkins]

Another reason for not resetting a code is that the car may be for sale and the owner is clearing the code temporarily to rip off a potential customer. I turned away one guy who was belligerent and swearing and yelling at all the other customers how we ripped him off because we wouldn't do a simple code reset and that "everyone else does it".



The rip off factor is one I never considered. It's sad that people do things like that.

[GScot]

Look into the OBD guide for the monitor system the MAP is tied into. It may be easier to just force conditions for that system to self-test which is probably drive cycles or worst case warm up/cool down cycles. That may be quicker than a full reset.

FYI check TX rules as they may allow a single monitor to be ready and not OK, basically any condition other than fail. I have an 03 Dodge with an intermittent fail on the EGR system. It usually decides to have that problem whenever inspection time comes around. As the EGR is one of the slowest to reset I can clear codes and do a short version of the OBD drive cycle which resets all but EGR leaving it on ready and head in for inspection giving me a pass with one monitor ready and the rest good.

[Fatty]

If you fixed the source of the trouble code, most likely the computer in that Chevy will reset itself after three or four restarts. That light may be out by the end of the day with just normal driving.

[Fatty]

I own a decent scan tool. Gave about a hundred for it a few years back. Good to have if you do anything in the garage besides oil and brakes. Now there are smart phone scan diagnostics. Interface at the OBD port and everything comes up on your phone. Might be the way to go.

[carpediemracing]

The rip off factor is one I never considered. It's sad that people do things like that.

I only realized that the guy in question was doing this based on comments he made under his breath. Then I realized that he was trying to sell the car and didn't want the CEL (or MIL) lit up. So I was okay with him being mad, I felt that was the right thing to do.

[carpediemracing]

Guys, I'm trying to get my inspection to pass and with all the smog restrictions in effect here in DFW, I need my check engine light to go off. I replaced my knock sensors yesterday (what a job!) and the SES light came back on today, so I feared I was going to have to take the manifold off again. Yikes! Luckily I went to AutoZone today and the code was actually 'low input' on the MAP (Manifold Air Pressure) sensor. Popped the hood, and it looks like I inadvertently pulled out an air hose as I was maneuvering the manifold back into place. Hose is now reinstalled, but how long might it take for the light to go off? Should I just reset the computer and drive the 50 miles to get all the sensors ready?

2001 GMC Yukon, 2WD, 5.3 V8.

Driving around should turn it off. Clearing it will force a new self test cycle, which probably takes longer.

I had a low something evaporative thing, it was cold related, and when I started the Expedition back up it was off. Checked codes, not there anymore. Probably something going south but for now it's okay.

[AngryScientist]

i bought a basic OBD scanner years ago and have used it many times. it cost about as much as a good ratchet wrench at the time, and just another one of the tools you pretty much need to own if you work on cars at all these days.

[shovelhd]

I am a VW guy so I have a Vagcom. It's VW specific, not cheap, but it's not just a reader, it's a full programming interface to the ECM. It's the best tool for VW diagnostics and customization. Resetting codes is a major part of diagnosis. Make sure whatever tool you buy can do it.

OP, are you sure the sensor just doesn't need to be cleaned?

[TronnyJenkins]

I am a VW guy so I have a Vagcom. It's VW specific, not cheap, but it's not just a reader, it's a full programming interface to the ECM. It's the best tool for VW diagnostics and customization. Resetting codes is a major part of diagnosis. Make sure whatever tool you buy can do it.

OP, are you sure the sensor just doesn't need to be cleaned?

I'm not sure, I just figured/hoped it had something to do with the air hose I unplugged. We shall see! I plan to try the drive cycle today.

[Tony T]

I'm not sure, I just figured/hoped it had something to do with the air hose I unplugged. We shall see! I plan to try the drive cycle today.

Try disconnecting the battery for a few minutes. That usually clears the check engine light
(however, if there's still a problem, the light will come back on)

[carpediemracing]

Today a guy came in with a Lexus he just bought. Check engine light went on shortly after he bought it. Looks like two bad catalytic converters. For a proper fix we're talking couple thousand dollars.

Based on how fast the light came on the seller reset the light prior to the test drive/sale.

I think if you buy any used car you should bring an OBD scanner and plug it in. If anything reads "Not Ready" then you know you have a problem.

[ultraman6970]

I do not know the car but I would say disconnect the battery and drive. Do you have the error number? depending on the car you might be getting that you are running lean... that could be the map (looks like you case) or even something so weird as the fuel pump or even the fuel filter that could be clog.

What's the error number you got? u had a line disconnected so might be it.

Disconnect the battery.

[TronnyJenkins]

Today a guy came in with a Lexus he just bought. Check engine light went on shortly after he bought it. Looks like two bad catalytic converters. For a proper fix we're talking couple thousand dollars.

Based on how fast the light came on the seller reset the light prior to the test drive/sale.

I think if you buy any used car you should bring an OBD scanner and plug it in. If anything reads "Not Ready" then you know you have a problem.

Man, that stinks. Duly noted!

I do not know the car but I would say disconnect the battery and drive. Do you have the error number? depending on the car you might be getting that you are running lean... that could be the map (looks like you case) or even something so weird as the fuel pump or even the fuel filter that could be clog.

What's the error number you got? u had a line disconnected so might be it.

Disconnect the battery.


Update to all- I finally got time on Saturday to dive into the issue. I took the engine cover back off, and the 'mechanic' that replaced the knock sensors (me) forgot to replace the wiring harness for the MAP sensor. That will do it EVERY time. Stupid me, but glad it is a free fix. Thanks for all the advice!