ASK THE AUTO DOCTOR
Q: I have a 2004 Ford Escape 2.0-liter with 300,000 miles. It's showing code P0401 problem in the EGR system. I have replaced the EGR valve, the vacuum regulator, and the pressure feedback sensor. When the vacuum hose is connected from the vacuum regulator to the EGR valve, the engine idles rough and almost shuts off, but when I disconnect the vacuum hose from the EGR valve, the engine idles fine. I put a vacuum pump on the EGR valve and pumped it up, but there was no change in the idle. It is still showing code P0401. Where do I go from here? Rick
A:
The EGR valve should not have any vacuum going to it at idle. EGR valves usually do fail on these engines. Plugged passageways in the intake manifold are the most common problem. EGR valve operation is electronically monitored, and a code will be triggered if it does not open or drop in vacuum. Both Alldata and Identifix have a trouble flow chart for step-bystep diagnosis.
Q: My 2007 GMC Envoy V-6 is displaying a check engine light and a lean code; when the temperature drops around 65 degrees then the same month rises back above 65 the check engine light goes out. The truck runs fine with the code on or off; on the highway I get up to 24 mpg. I do most of my repairs and did a tuneup, changed the oxygen sensors, and put injector cleaner in the gas. Hope you can help me with this ongoing problem. Jim
A:
The lean code can be caused by multiple problems including, but not limited to, a vacuum leak, coolant temperature, dirty or faulty mass air flow meter, leak after the mass air flow meter, carbon buildup, or dirty fuel injectors (cleaners may not clean all of them). I don't think your problem is fuel-pressure related. This may need the diagnosis of an ASE technician who will need to see when the computer sets the code and look at all of the sensor information. This is the only way to locate the problem; the live data is needed for all sensor values. The needed information can be found at Alldata and Identifix, along with sensor and component location.
Q: My 2007 Lexus GX 470 has 94,000 miles on it. The transmission is encased and there is no mention of changing its oil. I've called the local dealership where I bought the car. The customer service person told me to leave it alone unless I have problems, which I don't have right now. What do you recommend? David
A:
I always check the fluid condition and transmission operation before changing transmission fluid. On a lot of import vehicles, changing transmission fluid is a simple drain-and-fill procedure. When draining the fluid from the drain plug, only 3 to 4 quarts are replaced. I have never had a transmission failure after a simple drain and fill. I have also removed transmission pans (where possible), and replaced paper filters or cleaned metal screen filters. Note: the transmissions in vehicles from 1996 have multiple electronic solenoids and valve controls that depend on clean fluid and proper pressure.
Q: Recently, a reader commented his rain-sensing wipers don't wipe often enough. I have the same feature on both my 2017 CR-V and Audi A4. Both are adjustable via the switch near the steering wheel. I believe this has nothing to do with the body control module. Jim
A:
Yes, the wiper delay time is pre-set in the wiper control module. All vehicles with delay or intermittent wipers have an adjustment on the wiper stalk, lever, or knob. A driver can also simply set the wipers to the fixed-speed setting if they want.