Lately I have been getting a check engine signal so I decided to get the codes pulled down at the local auto parts store. the test gave two codes, #12: Idle speed control problem #41: No exhaust Gas Oxygen Switchd etected- always indicating lean. The second code makes sense, my car has been running very rich lately, if the computer reads lean it will richen the mixture..right? The idle speed control I don't know about, is it TPS related? Just wandering if anyone could help me get started int he right direction here with these codes or is more info needed? Thanks for any help.
Pulled engine codes...now what?
- Thread starter 89LXNotchPI
- Start date
DMAN302
My mom says thanks for the pearl necklace.
Check and clean the IAC, check voltage at TPS, check and clean 10pin connectors..just a start, but somethings causing the code. Sounds like your getting O2 sensor issues, they may need replacing, or the hego ground (orange ground wire near firewall) may have worked loose. Start there, and pull codes again.
txstang84
15 Year Member
you could always put a 12v source to it (after disconnecting it of course), and listen for it to open...
Code 41 or 91 - O2 indicates system lean. Look for a vacuum leak or failing O2 sensor.
The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel.
The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.
When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.
Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.
Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter.
Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer.
Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.
The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts
The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel.
The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.
When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.
Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.
Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter.
Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer.
Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.
The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts
Ok, a lot of this is greek to me, I get nervous when it is time to start checking voltages and resistances being that I don't have any experience with doing that, I don't think I am the only one on the site that feels this way. I definately will look into having that done. For now, is there any way to override/disable the signal sent from the O2's and have the computer run a "normal" fuel mixture? I know this isn't the right fix, but it might be the right fix for me. 
Also, the HEGO wire mentioned earlier, is that the same orange O2 wire richker talked about in his message? Thanks again, srry for being so dang clueless.
Also, the HEGO wire mentioned earlier, is that the same orange O2 wire richker talked about in his message? Thanks again, srry for being so dang clueless.
Step 1.) Find the instruction book that came with your Multimeter. Read it and familiarize yourself with how it works and how use it. If you lost the book or didn’t get one with it, do a Google search on the web to find the manufacturer’s web site & download a copy of the manual.89LXNotchPI said:Ok, a lot of this is greek to me, I get nervous when it is time to start checking voltages and resistances being that I don't have any experience with doing that, I don't think I am the only one on the site that feels this way. I definately will look into having that done. For now, is there any way to override/disable the signal sent from the O2's and have the computer run a "normal" fuel mixture? I know this isn't the right fix, but it might be the right fix for me.
Step 2. ) Make sure that you know what test lead plugs into which jacks on the Multimeter. There are usually several different jacks on most Multimeters, and they have different functions. Make sure that your battery(s) in the Multimeter are good: if you have any doubts, replace the battery(s).
Step 3.) Once you are sure that the Multimeter is functional and you have the leads plugged into the jacks for Ohms ( the upside down “U” symbol), do some simple measurements to make sure that you know how to use it correctly. Set the switch to the lowest range and touch the leads together: you should not see “nothing” but you should see 1.0-0.3 ohms. Measure a 60 watt light bulb: cold it will measure about 17.5 Ohms. It you measure it while it is hot, the reading will be greater.
Step 4.) Make several test measurements using the ohms function and the DC volts function. Remember all resistance measurements must be done with the power off the circuit. This avoids false readings and possible damage to the ohmmeter.. Repeat steps 3 & 4 until you are sure that you can do it without making any mistakes.
Step 5.) Then see http://www.autozone.com/servlet/UiB..._us/0900823d/80/19/59/5a/0900823d8019595a.jsp and carefully study ALL the information under the Heading Chassis Electrical, Basic Electricity – Understanding & Troubleshooting
Step 6.) Go back and carefully re-read both of my previous posts and download and print the diagrams from the link posted.
http://www.autozone.com/servlet/UiB..._us/0900823d/80/19/59/5a/0900823d8019595a.jsp for 89-93 model Mustangs
wiring diagrams.
Step 7.) Apply what you have learned and make the test measurements using the information in the wiring diagrams & my previous posts.
Here's a book that will get you started with how the Ford electronic engine control or "computer" works.
Ford Fuel Injection & Electronic Engine Control 1988-1993 by Charles Probst :ISBN 0-8376-0301-3.
It's about $20 from Borders.com see http://www.amazon.com/ . Select boo...very good, and I found it to be very helpful.
Similar threads
