CODES

Code 81 – Secondary Air Injection Diverter Solenoid failure AM2. The solenoid valve located on the back side of the passenger side wheel well is not functional. Possible bad wiring, bad connections, missing or defective solenoid valve. Check the solenoid valve for +12 volts at the Red wire and look for the Lt Green/Black wire to switch from +12 volts to 1 volt or less. The computer controls the valve by providing a ground path on the LT Green/Black wire for the solenoid valve.

With the with the ignition on, look for 12 volts on the red wire on the solenoid connector. No 12 volts and you have wiring problems.

With the engine running, stick a safety pin in the LT Green/Black wire for the solenoid valve & ground it. That should turn the solenoid on and cause air to flow out the port that goes to the pipe connected to the cats. If it doesn't, the valve is bad. If it does cause the airflow to switch, the computer or wiring going to the computer is not signaling the solenoid valve to open.

Putting the computer into self test mode will cause the solenoid valve to toggle. If you listen carefully, you may hear it change states.

If you have catalytic converters, you need to fix this code. If not you can use a TAB and TAD eliminator.

Code 82 – Secondary Air Injection Diverter Solenoid failure AM1. Possible bad wiring, bad connections, missing or defective solenoid valve. Check the solenoid valve for +12 volts at the Red wire and look for the Red/White wire to switch from +12 volts to 1 volt or less. The computer controls the valve by providing a ground path on the Red/White wire for the solenoid valve

With the engine running, stick a safety pin in the Red/White wire for the solenoid valve & ground it. That should turn the solenoid on and cause air to flow out the port that goes to the pipe connected to the heads. If it doesn't, the valve is bad. If it does cause the airflow to switch, the computer or wiring going to the computer is not signaling the solenoid valve to open.

If you have catalytic converters, you need to fix this code. If not you can use a TAB and TAD eliminator.

Both 81 & 82 codes usually mean that some uneducated person removed the solenoid control valves for the Thermactor Air system in an attempt to make the car faster. It doesn't work that way: no working control valves can cause the cat converters to choke and clog.

Code 10 is not a valid code for 5.0 Mustangs

Code 11 means the computer's internal self tests passed, and that any problems present are in the external sensors and wiring.

Code 41 or 91 Three digit code 172 or 176 - O2 sensor indicates system lean. Look for a vacuum leak or failing O2 sensor.

Revised 22-Jun-2009 to include 3 digit code and wiring for 94-95 5.0 Mustangs

Code 41 is a RH side sensor,
Code 91 is the LH side sensor.

Code 172 is the RH side sensor
Code 176 is the LH side sensor

The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned 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

Testing the O2 sensors 87-93 5.0 Mustangs
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. The O2 sensor voltage should switch between .2-.9 volt at idle.


Testing the O2 sensors 94-95 5.0 Mustangs
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 red/black wire) and 27 (RH O2 with a gray/lt blue wire). Use pin 32 (gray/red wire) to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


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.

Testing the O2 sensor wiring harness
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.

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

Make sure you have the proper 3 wire O2 sensors. Only the 4 cylinder cars used a 4 wire sensor, which is not compatible with the V8 wiring harness.

Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.

If you get only code 41 and have changed the sensor, look for vacuum leaks. This is especially true if you are having idle problems. The small plastic tubing is very brittle after many years of the heating it receives. Replace the tubing and check the PVC and the hoses connected to it.
A secondary problem with only a code 41 is for cars with an intact smog pump and cats. If the tube on the back of the heads clogs up the driver’s side, all the air from the smog pump gets dumped into one side. This excess air upsets the O2 sensor calibration and can set a false code 41. The cure is to remove the crossover tube and thoroughly clean the insides so that there is no carbon blocking the free flow of air to both heads.


If you have a MAF present, but it isn't hooked up, watch for a 66 code. Since you didn't list 66 as one of the codes, that means you have a speed density computer. Make sure that the MAP sensor (small black box mounted on the firewall behind the uppper intake manifold) is connected to engine vacuum.

I am sure that someone here can probably post a better Speed Density explaination than I can, but here, goes.

Speed Density uses input from the MAP sensor (manifold vacuum), ACT (air temp), TPS (throttle position), O2 (oxygen sensor), and ECT (engine coolant) to arrive at a guess as to how much fuel is required to make the correct air/fuel mixture. Engine vacuum is the primary guide to what calculations to make to arrive at the amount of air that is entering the intake. Based on input from the sensors, the Speed Density calculates an open pulse time for the fuel injectors. The change in pulse time changes the air/fuel mixture. The problem arises when the engine's airflow input exceeds the lookup table's expectations, or the vacuum is radically different from the table specs. Speed Density's problem is that it has no way to measure airflow entering the intake, so it makes an educated guess based on sensor input.

Mass Air Flow (MAF) is used to help the computer measure the amount of air entering the intake so that it knows how much fuel the engine needs to perform properly. Mass air flow measures not only the amount of air, but to a limited extent, also its density. Changes in humidity, barometric pressure and inlet air temperature also affect air density. The Barometric Atmospheric Pressure or BARO sensor measures the barometric air pressure. The ACT sensor measures the inlet air temperature. Using the input from these three sensors helps the computer actually calculate the air density, The air/fuel ratio is calculated on the basis of air density, so the MAF, BARO, ECT, O2, TPS & ACT sensors work together to make it happen. The computer uses the sensor data to calculate an open pulse time for the fuel injectors. The change in pulse time changes the air/fuel mixture. Mass Air accomodates changes in airflow because it measures the airflow. It is not concerned about manifold vacuum, so a wild cam with poor idle vacuum and characteristics doesn't make it do strange things.

The MAF output varies with RPM which causes the airflow to increase or decease. The increase of air across the MAF sensor element causes it to cool, allowing more voltage to pass and telling the computer to increase the fuel flow. A decrease in airflow causes the MAF sensor element to get warmer, decreasing the voltage and reducing the fuel flow.

Code 10 is a Seperator code. Everything after this code is the Continuous Memory codes the system has logged over time.

Usually when the KOER test want start, it because of another Fault Code. This car an Auto or 5 speed?

Ive seen the ECM's flash a 6 cylinder ID code, but still throw codes. Not sure if its just a glitch or not.

What are you using for a Scan Tool? One from the Parts store?

Leave the store scanner alone.

In the picture below, run a jumper from the STI terminal to the SIGRTN terminal. Then hook a test light to the positive side of the battery of starter solenoid with the clip, and use the probe of the test light installed in the STO teminal on the diagnostic connector. Turn the key on, and run both KOEO and KOER test.

Brando5641 said:

What is a test light???



LOL jk i dont own a test light. Can you do it with a Volt Meter?

Can some one post a link for that TAD elm. instrustions plz? I for some reason cant find it and i just seen it the other day.

Click to expand...

Volt meter is harder to read the codes with. Just go this route. Using the same picture above... Just run the jumper from the STI to the SIGRTN. Then sit in the drivers seat and count the flashes from the Check Engine Light after you start the car. And make sure its up to operating temp when the test is ran.

TAD? You mean the Thermactor Air Diverter?

Are you running the SMOG system?

An 02 can not have power and show lean, it can go bad and show lean........Just depends

Flashes for 91 would be 9 flashes......Pause.....1 flash

Since the smog system is not being used, dont worry about the Thermactor Codes unless your running Cats

This is the best i can do, and it isn't exactly what you need...

The following is a view from the computer side of the computer wiring connector.


Pin 29:
When you look at this thing from the wiring side, it is the center row of pins om the RH side. It is 1 pin away from the center bolt.

Find pin 29 and pin 27 is near it.

TPS testing:
Most of the time a failed TPS will set code 23 or 63, but not always. Use either an analog meter or a DVM with an analog bar graph and connect the leads as instructed above. Turn the ignition switch to the Run position, but do not start the engine. Note the voltage with the throttle closed. Slowly open the throttle and watch the voltage increase smoothly, slowly close the throttle and watch the voltage decrease smoothly. If the voltage jumps around and isn’t smooth, the TPS has some worn places in the resistor element. When the throttle is closed, make sure that the voltage is the same as what it was when you started. If it varies more than 10%, the TPS is suspect of being worn in the idle range of its travel.

TPS Troubleshooting:

The TPS sensor is a variable resistor like the volume control on most cheap radios. We have all heard them make scratchy noises as you turn them up or down. The carbon element can wear and cause a drop out spot in the output voltage. This confuses the computer because it expects to see a steady TPS voltage increase as the Throttle opens up.

Wire colors & functions:
Orange/white = 5 volt VREF from the computer
Dark Green/lt green = TPS output to computer
Black/white = Signal ground from computer

TPS troubleshooting steps:
1.) Use the Orange/white & Black white wires to verify the TPS has the correct 5 volts source from the computer.
Use the Dark Green/lt green & Black/white wires to set the TPS base voltage. Setting the TPS: you'll need a good Digital Voltmeter (DVM) to do the job. Set the TPS voltage at .5- 1.1 range. Because of the variables involved with the tolerances of both computer and DVM, I would shoot for somewhere between .6 and 1.0 volts. Unless you have a Fluke or other high grade DVM, the second digit past the decimal point on cheap DVM’s is probably fantasy. Since the computer zeros out the TPS voltage every time it powers up, playing with the settings isn't an effective aid to performance or drivability. The main purpose of checking the TPS is to make sure it isn't way out of range and causing problems.
2.) Use an analog voltmeter to check the voltage on the Dark Green/lt green & Black/white wires to make sure that it increases smoothly and doesn’t drop out or increase suddenly.

Some basic checks you can make to be sure that the sensor is getting power & ground:
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.
Check the resistance between the black/white wire on the MAP/BARO sensor and then the black/white wire on the EGR and the same wire on the TPS. It should be less than 1 ohm. Next check the resistance between the black/white wire and the negative battery cable. It should be less than 1.5 ohm.

The following power on check requires you to turn the ignition switch to the Run position.
Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or EGR sensors. Use the black/white wire for the ground for the DVM.

Change the fuel filter. And look at you basic ignition parts.


Is the MAP sensor hooked to vacuum?