Tip & How-To about Nissan Maxima

P0420 - P0430 - P0100 - P0105 : The Top Four Money Pit Codes


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Does your vehicle's computer tell the truth, or can it be deceptive? Actually it receives information from a variety of sensors and they can be deceptive. The average auto mechanic does not delve deeply into OBDII codes. A P0420 - P0430 are pointing at the catalytic converter, and changing the Oxygen Sensors would be the major choice. I have lost count of the number of times this solution failed. The cost of one oxygen sensor can average $150, add the cost of labor and your looking at $300 tossed into the money pit.

The oxygen sensor can be tricked by a misfire. A misfire places oxygen into the exhaust manifold. The sensor detects a lean condition and signals the ECM to send more fuel. An O2 sensor can become contaminated due to an air leak (hole in the exhaust system), vacuum leaks, leaking fuel injectors, defective canister purge valve, fuel introduced into the canister, excessive fuel pressure, or a defective MAP (manifold absolute pressure) sensor. Fortunately the O2 sensor can be cleaned. However, remember if the condition that caused the fouling isn't cleared , they will again become contaminated.

Radio Shack sells a product designed to clean electronic parts. The catalog # is 640-4338. The name is DOXIT and the cost is $14.99. Included is a can of gold contact point cleaner. This product leaves no residue and can be used to clean O2 and other sensors.Disconnect the positive battery cable. Remove and clean (follow directions on the can) the O2 sensors. Before reinstalling, wire brush the base of the O2 that contacts the exhaust port, wire brush the exhaust port to insure proper grounding; Also spray the male and female connector pins.Reconnect the positive battery cable and test drive the vehicle. If the code does not return; $14.99 was much easier on your wallet than $300.

The next money pit candidate is the MAP (Manifold Absolute Pressure) sensor. Trouble codes may or may not be stored in diagnostic memory.
Codes P0100 - P0105 indicate a problem with the MAP. An auto mechanic may suggest changing the sensor. The average cost is $140. He may be correct, however in many instances The MAP is not telling the truth. This sensor can tell a lie if the exhaust system is restricted, it's vacuum line is pinched, kinked, split, loose, or deteriorated or a low vacuum signal exists. Always rule out the the obvious before changing the MAP .

Symptoms such as poor acceleration, hard starting, rough idle, or just plain won't start may occur without setting the check engine light. This is a part pulling mechanic's dream; Money pit heaven! All parts in today's world are are very costly. Before you sputter and spit your way down to Mr. Part Pullers Garage, try localizing the fault on your own.

The MAF (Mass Air Flow Sensor) measures the volume and density of air entering the throttle body. The ECM uses this information to calculate the correct amount of fuel to deliver to the engine.MAF sensors are either "hot wire" or "hot film". Hot wire can be tested using a volt meter whereas hot film can not. Output at idle is .4 to .8 volts increasing to 4.5 to 5.0 volts at wide open throttle. To simplify; Voltage increases as engine rpm increases. This sensor is a common cause of symptoms listed in the above paragraph, Follow the exit of the air filter box, the MAF is between that point and the intake. It has a connector on it's side or top. Remove the sensor, be careful they are easily damaged. Check that the hose in and hose out are free of any rips or holes; This allows dirt to enter and contaminate the sensor. Also, if you are using an aftermarket oil impregnated air filter be advised the oil will contaminate the sensor. Both hot wire and hot film can be cleaned using DOXIT spray. Clean both sensor and associated male and female pins, replace and test drive the vehicle. If you notice immediate performance improvement; Feel proud!

Check vacuum lines at the throttle body. This is a major distribution point of lines that run critical sensors. Loose, broken, poorly seated, and worn lines will cause multiple faults that beckon the money pot.

Check the PCV valve and it's vacuum line. PCV's are well hidden in today's engines, and are "push and twist" to remove. Most cars have a vacuum routing diagram under the hood. locate the vacuum line that controls the PCV and trace it to the valve. When you remove it, give it a shake and you should hear the little ball that lives inside rattle around; This indicates valve is good. If you replace the PCV, look at the old one to see if it has an "O" ring on it; Make sure you put the ring on the new valve.

Check for correct fuel pressure. I have found that asking your local dealer's service department for the psi reading of your car usually works. You can rent a fuel pressure gauge at an auto parts store. Poor fuel pressure can be caused by several faults. The main causes are; The pump, vapor canister purge not opening and a defective TPS(Throttle Position Sensor).
The TPS can be tested with a volt meter; At idle meter should read below 1 volt, as throttle is increased voltage should rise smoothly to 4 volts. If the voltage skips or jumps as you increase the throttle the TPS is defective. A bad TPS will affect fuel economy, put the idle speed in a hunting mode, and cause a timing variation.

The last money saving tip concerns proper grounding. I have come across vehicle's that have codes P0420, P0430, and run poorly. Sensors are sensitive to small variations in current flow. There is a lot of plastic in today's vehicle's, and and proper grounding is essential to trouble free operation. Using an ohm meter set on theX10 scalemeasure from the engine block to the body; making sure your probes are on bare metal. You should read zero ohms (full deflection) any reading at all is not acceptable. Measure from the body to the negative post on the battery. You should also read zero ohms.

If you do not read zero ohms, ground straps need to be instaled. Use #8 stranded wire. Find a bolt on the engine block and one on the body (radiator mounting bracket is a good choice). Choose a ring connector that fits the selected bolts and solder them to both ends of the strap.Next, choose a larger ring connector that will fit the outside of the negative battery cable bolt and solder it to one end of the second strap,solder a ring connector to the other end. Remember, where you bolt these straps the surface must be bare metal.

Readings on several vehicle's that had P0420, P0430, and ran poorly ranged from 2,000ohms to 5,000ohms. After the installation of ground straps the codes cleared and the engine ran silky smoth. The cost was $5. I shudder to think how much money those owners would have spent at Mr. Parts Puller's Garage.

Don't pour your hard earned cash into "The Money Pit".


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