Apparently these cars have an issue where the EGR ports in the intake manifold become clogged with carbon.
People recommend having the intake manifold cleaned and these ports cleaned at most every 100,000 miles, if not the whole EGR system.
The problem is that unlike most other cars that connect the EGR next to the throttle body where the exhaust gas flows with the rest of the air in to the engine, the 3rd generation Prius has a small port for each cylinder in the manifold. One of these ports will clog first, cutting that cylinder off from the EGR system, and diverting the rest of the exhaust gas in to the remaining cylinders. I believe this does not trigger a fault code. This leads to prolonged overheating of the affected cylinder and eventual engine damage and/or head gasket failure.
I’m surprised that a blocked EGR can do this. They must run the engine borderline too lean for fuel economy to begin with. I know little about EGR, but I don’t think other vehicles have separate per cylinder ports for EGR that can clog like this. So a clogged EGR can be detetected and/or corrected by the oxygen sensor without damaging just one cylinder while the problem goes undetected.
A lot of these cars still have under 200k miles on them. In the next few years this might became a much bigger issue, given the number of people who don’t research preventative maintenance. This just happened to someone I know with about 260k miles.
Thank you for this alert and description of an EGR system with individual ports feeding each cylinder. It was a fun trip down memory lane to think back to 25 years ago when this was news.
Below is the service bulletin associated with the EGR problem.
Some 2010 – 2015 model year Prius (2ZR-FXE equipped) vehicles and 2012 – 2015 model year
Prius PHV and Prius V (2ZR-FXE equipped) vehicles may exhibit a “runs rough” and/or MIL “ON”
condition with DTC(s) P030# (Misfire) during light acceleration while the Exhaust Gas
Recirculation (EGR) system is active. Replace the intake manifold assembly to address
this condition.
That indeed does seem like a bad design. My truck’s single EGR passageway carbon-clogs about every 50K miles or so, then I have the chore to clean it out. I presume the engineers at Toyota thought the engine was so clean at burning gasoline that small diameter EGR passageways would never clog. But if some of them do clog, I can see how diagnosing the problem could be very difficult. My Corolla’s EGR passageway (I believe it has just one) has never clogged in over 200K miles.
Probably not. The main immediate effect would be an increase in the amount of N-compound air pollution. But if the Corolla was driven hard, a lot of rapid uphill accelerations, that might cause the internal engine parts to get hot enough to eventually cause a failure.
The EGR is used at full throttle, when the engine is under higher load conditions, such as accelerating or climbing hills. I don’t believe it’s needed at all under partial load.
I believe you’re right. Two areas where EGR functionality has changed over the years seem to be:
During hard acceleration when you need full power, EGR is disabled so full power isn’t reduced.
In steady state part-throttle conditions, the ECU will lean out the mixture which causes high combustion temperatures. EGR is partially enabled then to minimize NOx formation. [@TheWonderful90s: I stand corrected.]
