EGR flow P0401 & P0402
Good afternoon fellow automotive technicians,
The guys at the shop passed this vehicle on to me after they've replaced a couple of items already and also are out of ideas in the meantime. I have gone over the EGR hose routing and everything looks good. I've noticed while test driving that when going up any steep hills the vehicle bogs down tremendously.
The parts that have been replaced to try to eliminate the P0401 code are: EGR valve, EGR vsv, downstream oxygen sensor, map sensor (used replaced due to previous map related code)...
I checked the vehicle this past week quickly, after starting a hotline repair via Identifix - and the technician told me to carefully look at oxygen sensors... I did and noticed that the rear oxygen sensor when we open the EGR shows rich, and when we manually close EGR it reads lean... Long term fuel trim shows -10 % on average and so it is thinking that it is receiving too much fuel... Front oxygen sensor looks a bit lazy but functional and it also looks to have been replaced recently but customer nor shop have any record of the replacement.
I will take screen shots, as I don't know how to transfer files from the Verus to the files here for our discussion.
I noticed that the vehicle consumes oil as well - has to be re-filled each week, ~ 0.5 to 1 quart of oil when driven ~ 300-500 miles each week.
Again, any input would be appreciated.
Without any system info in front of me, just using what info provided, seems like the EGR system has some influence from back pressure. Was a back pressure reading taken on the vehicle?
- Can you stall the car by operating the egr?
- Did you smoke the intake for vacuum leaks?
- Did you check the exhaust for leaks?
All of these can skew readings.
I don't know what the EGR test strategy is used on these but given the oil consumption issue and lack of scoot, is wanna rule out a blocked cat.
How about a back pressure test?
You may also wanna look for carbon blocked EGR passages but that wouldn't cause your lack of power
Check for clogged passages on the throt body . If you can bidir controll it open and it doesn’t stumble or stalle out. It’s probably clogged up
I can't remember with 100% certainty which EGR design this engine has. It has been a few years since I have seen one. But if I remember correctly, it MIGHT have a temperature sensor that screws into the EGR to let the engine computer know that the EGR is properly working.
One thing that I do know is a high failure part on the … EGR systems from the 90s is the vacuum modulator. The diaphragms always went bad. Id check those two items, assuming the electrical to the vsv was checked.
The MAP and the EGR codes together along with the symptoms lead me to advise you to check back pressure. The MAP should be around 1.5v at idle and increase gradually. If you crack the throttle does the MAP voltage heads rapidly toward 3.5v? If it does, it leads me to the exhaust side.
The EGR Monitor on this is measured through the MAP Sensor at a steady cruise. Any excessive backpressure could give this results you are experiencing. The backpressure could keep the EGR Transducer open if there is excessive backpressure. These transducer filters also plug up and hang the EGR after they commanded open.
Any chance to get an update on this vehicle? This is supposed to be a vehicle that uses a vacuum modulator. The modulator sets the AMOUNT of EGR valve movement by changing the level of vacuum available. The VSV EGR allows the vacuum supply based on ECM operation. The fact that the flow is coding for both excessive AND insufficient would point me to the modulator for testing....... All other comments about engine condition are valid for cause, however you did not mention the oil loss location. Is it leaking, consuming or both? Either way, the post by Pj is a clue. Toyota has used several different designs of EGR and the diagnosis for each is slightly different.