Despite check-engine light, valve may not need replacement

  • Article by: PAUL BRAND , Star Tribune
  • Updated: January 16, 2011 - 3:46 PM

QI have a 2007 Dodge Grand Caravan with the "check engine" light on. I checked it with a code reader and got a P0404 code: "Exhaust Gas Recirculation Circuit Range/Performance." A new EGR valve costs $80. Is there any way to clean or fix it and turn off the light?

ANotice that the code does not say "faulty EGR valve." The P0404 code indicates the powertrain control module (PCM) is not seeing the EGR sensor performance or position that it expects to see. This could mean a clogged EGR tube, a faulty EGR sensor or harness or a problem with the electronic EGR valve itself. There is no specified service for these components, but you could remove the valve and tube to inspect for carbon buildup that may be blocking the flow of recirculated exhaust gases.

If the problem is corrected, the check-engine light may turn itself off after a number of key cycles without seeing the fault. Otherwise, you would need to scan tool to reset the system. Some auto-parts stores offer code reading and reset service at no cost.

QI'm losing heat from my 2000 Dodge Durango. The heat gradually decreases until there is nothing but cold air. When the car idles, the air gets cool and then warms up when I increase the RPM. I took it to a mechanic and explained the problem. The shop flushed the heater core, replaced the timing cover and installed a new 195-degree thermostat. The heater core and water pump were replaced within the past two years. I am still not satisfied with the heat. What is the next step?

ADoes the vehicle lose or consume any coolant? A cylinder head gasket or intake manifold gasket leak may allow the coolant level to drop enough to introduce air into the system. This could stall the flow of coolant, causing heating fluctuations. A chemical test for the presence of exhaust hydrocarbons in the coolant might confirm a head gasket issue.

An often-overlooked potential cause is a fault radiator pressure cap. If the cap fails to hold pressure -- typically between 12 and 16 pounds per square inch -- coolant can be pushed out of the radiator and into the recovery tank and not be drawn back into the system. Again, this may allow air in the system, slowing coolant flow to the heater core.

And finally, a repeated bleeding of the cooling system might expel any trapped air and improve heater performance.

QWe have a 2004 Prius that we have driven more than 106,000 trouble-free miles, except for replacing a water pump at 82,000 miles. Now we have received a recall from Toyota to take our car to our dealer to have the water pump replaced at no charge. The dealer says this is not the same mechanical water pump we replaced earlier. Are there really two water pumps in a Prius?

AYes. Your hybrid-powered vehicle has both a small gasoline engine and an electrical motor drive system. Each has its own, separate cooling system. Apparently, the mechanical water pump for the gasoline engine has already been replaced. Now, Toyota is replacing the electrical "coolant heat storage pump" for the electrical power inverter that converts high-voltage DC current into AC current to power the motor and generators. This pump cools the power inverter and is integrated into the powertrain control system.

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