How to check Lambda Sensor?
How to check Lambda Sensor?
How can i check my Lambda sensor as the car has started using a lot more fuel recently?
Also where is the Lambda sensor located?
I have checked the MAF and that is fine.
Also where is the Lambda sensor located?
I have checked the MAF and that is fine.
Scooby Regular
Joined: Apr 2005
Posts: 307
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Originally Posted by scoobboy
Cheers mate, how do you know if its not working correctly then?
Lambda sensors can be tested either on or off the car. Both methods have their advantages. Testing the sensor off the car enables you to check the sensor itself without interference from other components. Testing the sensor on the car shows you what is going on in the real-life situation.
Before testing the sensor on the car you must make sure that the engine is thoroughly warm (leaving it to idle won’t do – take it for at least a 10 minute drive) and that it has no misfires or leaks in the exhaust system between the engine and the lambda sensor.
Warning
For both tests you need a good quality digital multimeter with a high impedance (at least 1,000,000 ohms/volt – most digital multimeters meet this requirement). Do not use an analogue meter – they will not give accurate results and can damage the sensor. Many digital multimeters don’t react quickly enough to the rapid changes in output from the sensor and so I use a simple home-made tester which has LEDs to indicate voltages between 0 and 1.2 volts. (Separately I will put up details of how to build this).
On Car Test
The lambda sensor used on the your car has 3 wires – two white heater wires and one black signal wire. Generally it is best to tap into the wires using wire piercing test probes which makes a tiny hole in the insulation. I make the connection at the car side of the plug where the leads from the sensor join the main loom because the wires attached to the probe are sheathed in a very hard heat proof insulating material which is very difficult to puncture. If when you switch on the ignition you get a reading of 12+ volts you have tapped into the heater power lead by mistake.
For this test you must leave the sensor connected to the ECU. Connect the positive multimeter probe to the sensor output wire and the negative probe to earth. With the engine running if all is well the voltage shown on the meter should flicker up and down the scale changing at least twice a second between about 0.1 and 0.8 volts -- the average reading should be about 0.4-0.5 volts but it should never be steady at this voltage. Flick the throttle open and the voltage should flicker, rise for a second or so then fall again. This indicates the ECU is receiving input from the sensor and is responding properly.
A steady voltage of between 0.4 and 0.5 V is a sign that the ECU is running in open loop mode . Either the engine is not fully warm or it may indicate a bad connection or a faulty water temperature sensor or an ECU fault. It could also indicate a problem with the sensor heater so check the heater is getting power and is properly earthed.
Workbench Testing
Use a good digital multimeter. Clamp the sensor in a vice or use pliers or vice-grip to hold it. Clamp the negative multimeter lead to the case and the positive to the output wire. Use a propane torch and apply the inner blue flame tip to heat the fluted or perforated part the sensor. You should see a DC voltage of at least 0.6 within 20 seconds. If not, the most likely cause is open circuit internally or lead fouling. If OK so far, remove from flame. You should see a drop to under 0.1 volt within 4 seconds. If not the sensor is probably silicone fouled (coolant leak?). If still OK, heat for two full minutes and watch for any drop in output voltage. Sometimes, the internal connections will open up under heat.
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