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So my check engine light came on about 5 minutes after driving away from the shop that replaced a faulty heater core today. I'm planning to give the shop a call tomorrow to see if they can check it out quickly, but any ideas on what might be the cause? I've put about 2,000 miles on it since the last oil change and about 1,000 miles since the last tune-up. Both of the those jobs were done at Toyota dealer shops, but the heater core job wasn't. What are the chances something got disturbed during the heater core installation? Or is it possible I just need to do a reset? For this model, does turning the car on and off three times in quick succession reset the light?
 

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Something was left disconnected, I'd guess. You can have the codes scanned at AutoZone. But check your fluids before going anywhere.
 

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Something was left disconnected, I'd guess. You can have the codes scanned at AutoZone. But check your fluids before going anywhere.
I suspect so too. The shop asked me to bring it back, but I'll probably do an AutoZone scan first just so I know what they're going to see (need to pick up a few things there anyway).

There was an after-market alarm system that they left disconnected (because I misplaced the one keyless entry remote that came with the vehicle). Surely leaving that disconnected wouldn't have caused the light to illuminate?
 

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So I had Autozone do a scan, and it came back as P0401- Exhaust Gas Recirculation insufficient flow detected. What's the likelihood that the heater core replacement damaged either the EGR Modulator Valve or a connecting part? Or is this likely purely coincidental? Could the work have disturbed something that was close to breaking anyway? Any idea what a repair should cost?
 

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P0401 could be accidentally caused by replacing the heater core. In connecting the heater hoses at the firewall, it would be possible to knock off a vacuum line to the EGR VSV which sits just below the intake manifold between cylinder 2 and 3. Double check the other EGR vacuum lines between the throttle body and the EGR modulator and EGR valve. If they are cracked or damaged, they could cause this too.

The P0401 could also be caused because the EGR Vacuum Solenoid Valve has actually failed. These do fail from time to time. Labour to replace the VSV on my 2wd '97 was 0.3 hours so easier to let the mechanic do it than fight with it myself. 4WD models are more difficult to change. There are a number of threads of how to change the VSV on a 4wd Rav but again check the book rate and see if it is worth doing yourself. The easiest way is to put the car on a lift and using a long socket extension to take out the one bolt from underneath, beside the catalytic converter. A new VSV at Toyota is fairly expensive, but might be worth it. I bought one from Rock Auto that was much less expensive a year ago and it looked the same visually as the Toyota unit and has worked so far.

The EGR system is worth fixing as it affects fuel economy negatively when it doesn't work. The EGR VSV also shuts off the EGR when the coolant is cold. If the valve fails you get EGR when cold which makes it not run as nicely until it warms up.
 

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P0401 could be accidentally caused by replacing the heater core. In connecting the heater hoses at the firewall, it would be possible to knock off a vacuum line to the EGR VSV which sits just below the intake manifold between cylinder 2 and 3. Double check the other EGR vacuum lines between the throttle body and the EGR modulator and EGR valve. If they are cracked or damaged, they could cause this too.

The P0401 could also be caused because the EGR Vacuum Solenoid Valve has actually failed. These do fail from time to time. Labour to replace the VSV on my 2wd '97 was 0.3 hours so easier to let the mechanic do it than fight with it myself. 4WD models are more difficult to change. There are a number of threads of how to change the VSV on a 4wd Rav but again check the book rate and see if it is worth doing yourself. The easiest way is to put the car on a lift and using a long socket extension to take out the one bolt from underneath, beside the catalytic converter. A new VSV at Toyota is fairly expensive, but might be worth it. I bought one from Rock Auto that was much less expensive a year ago and it looked the same visually as the Toyota unit and has worked so far.

The EGR system is worth fixing as it affects fuel economy negatively when it doesn't work. The EGR VSV also shuts off the EGR when the coolant is cold. If the valve fails you get EGR when cold which makes it not run as nicely until it warms up.
Thank you. This is very helpful. I agree it needs to get fixed sooner rather than later - not only for the fuel economy but also because I'd be sure to fail an emissions test where I live (Illinois) with that malfunctioning.

Should I trust a non-Toyota dealer shop to fix this? The shop that replaced my heater core wasn't a dealer, and they did a fine job with that (from what I can tell - the heat works!). They've got great reviews. I like my Toyota dealer, but I always leave feeling like I paid more than I should and that they're more interested in getting me to trade my vehicles in on something new than in servicing old vehicles (we have a 2007 RAV4 in addition to my 2000).
 

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Okay, so this is embarrassing. I just checked over the service records from all the maintenance I had done at my local Toyota dealer shortly after I purchased this vehicle last August. The EGR Valve Assembly, EGR Vacuum Module and VSV Vacuum Switching Valve were actually all replaced at that time. So it has to be the vacuum lines, right? If the new parts are bad already, they should surely be under warranty by Toyota, right? Unless they were damaged during the heater core installation? In that case, I would assume the repair shop would be on the hook for it?

Since I know the parts are all new, I'll take it back to the same shop that just did the heater core. Should I assume that they won't charge anything for this visit, either because they were negligent in not hooking up the vacuum lines or in the unlikely event they damaged something? Would I be justified in pushing back if they do charge me?
 

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Okay, so this is embarrassing. I just checked over the service records from all the maintenance I had done at my local Toyota dealer shortly after I purchased this vehicle last August. The EGR Valve Assembly, EGR Vacuum Module and VSV Vacuum Switching Valve were actually all replaced at that time. So it has to be the vacuum lines, right? If the new parts are bad already, they should surely be under warranty by Toyota, right? Unless they were damaged during the heater core installation? In that case, I would assume the repair shop would be on the hook for it?

Since I know the parts are all new, I'll take it back to the same shop that just did the heater core. Should I assume that they won't charge anything for this visit, either because they were negligent in not hooking up the vacuum lines or in the unlikely event they damaged something? Would I be justified in pushing back if they do charge me?
The work from the Toyota dealer is probably not under warranty anymore, because most dealers only warranty for 12 months, unfortunately. But it is very likely, from what you described, that this is just a vacuum hose that was accidentally disconnected during the heat core work, as LugNut and cRAVe said. If you'd like to check yourself, here is a video which shows where the EGR valve is, and you can see that there are a few vacuum hoses. The two large hoses that go through the firewall (into the cabin) are the heater core hoses, so you can see that it would be possible for something to happen, since this is a small space. Skip to 01:47 in this video:


The shop should remedy this for you, free of charge, and they will probably just find the hose and reconnect it.
 

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The work from the Toyota dealer is probably not under warranty anymore, because most dealers only warranty for 12 months, unfortunately. But it is very likely, from what you described, that this is just a vacuum hose that was accidentally disconnected during the heat core work, as LugNut and cRAVe said. If you'd like to check yourself, here is a video which shows where the EGR valve is, and you can see that there are a few vacuum hoses. The two large hoses that go through the firewall (into the cabin) are the heater core hoses, so you can see that it would be possible for something to happen, since this is a small space. Skip to 01:47 in this video:


The shop should remedy this for you, free of charge, and they will probably just find the hose and reconnect it.
So the vacuum hose was the problem, and they quickly remedied it free of charge.
 
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