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Toyota Camry Failed for High CO Could It be the MAP?

Hello,

My 97 Toyota Cmary just failed the emission for high CO levels at 15 Mph in retest. It failed at both speed for CO levels in the first test. Here are the no's for the first test.

15 MPH

CO2% 15.1

O2% 0.0

HC 40PPM (55 MAX) pass

CO 0.89 (0.50 MAX) fail

NO 4 (437 MAX) pass

25 MPH

CO% 15.0

O2% 0.0

HC 32PPM (39 MAX) pass

CO 1.01 (0.48 MAX) fail

NO 3 (437 MAX) pass

I had replaced the air filter and o2 sensor before the test. After the test I replaced Coolant temperature sensor and TPS sensor. I also replaced Idle Air Control Valve as i had to take the throttle assembly apart to install the TPS sensor. I didn't replace the Map sensor as it was expensive and no aftermarket was available. In the retest it passed the CO levels at 25 Mph and numbers improved significantly for CO and HC. But it still failed at 15 Mph and numbers remained almost same. Here the no's for second test.

15 MPH

CO2% 14.7

O2% 0.0

HC 39PPM (55 MAX) pass

CO 0.89 (0.50 MAX) fail

NO 1 (437 MAX) pass

25 MPH

CO% 15.1

O2% 0.0

HC 18PPM (39 MAX) pass

CO 0.23 (0.48 MAX) pass

NO 0 (437 MAX)pass

Do you think looking at the above no's that it is MAP sensor malfunctioning at low speed or some thing else? Please help. Thanks.
Answer:

It looks like you've already replaced all the main air/fuel mixture control sensor... except the very important, MAP sensor. We'd recommend inspecting the MAP for proper operation and if found defective going ahead with replacing it. The MAP (manifold absolute pressure) sensor is the main component, which along with the TPS, is used to determine air/fuel ratio during idle and off idle engine conditions. The oxygen sensor(s) main role is to fine tune the air/fuel mixture after an initial setting is determined. When seeing CO numbers as high as .89 it is always best to suspect a faulty MAP sensor before the oxygen sensor(s). MAP (Manifold Absolute Pressure) Sensor - The MAP sensor should be checked for proper operation. The MAP (manifold absolute pressure) sensor is responsible for letting your Toyota Camry ECM (engine control module) know how much intake vacuum exists. This sensor plays a crucial role in determining proper air/fuel mixture ratio at both idle and off-idle conditions. How to Test the MAP Sensor - You may test the MAP sensor using a voltmeter (setting on voltage measurement). You should see an increase in voltage as RPMs increase (intake vacuum decreases). At idle you should see between to 1 to 1.5 volts. Off idle, voltage should start increasing to a maximum of 5.0 volts. The measurement should be taken from the middle wire (should be black/yellow) of the three wire connector at the MAP sensor. You must leave the MAP sensor connected during this test, and back probe the connector. If you have a hand vacuum pump, you may use it to apply vacuum to the sensor, as opposed to running the engine. Disconnect the vacuum line leading from the intake manifold to the sensor and attach your hand vacuum pumps vacuum line instead. Turn your Camry's ignition on, do not start the engine, and conduct the MAP sensor test. If no voltage exists, either at no vacuum or 20in HG vacuum, inspect the other two wires for power and ground. Red wire should have 5 volts while the ignition is on. Brown wire should be ECM ground. posted by SmogTips Support

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