The OBD-II system allows for many engine components to be monitored to ensure proper operation. When the PCM interprets a value that is outside of the normal specifications for a given component, the check engine light will illuminate and a diagnostic fault code will be stored. These stored diagnostic codes can greatly aid in identifying and fixing a faulty engine component.
By Joseph Coelho — October 6, 2015
This article applies to the V6 Ford Mustang (1994-2004).
The on-board diagnostic (OBD) system was developed for manufacturers to monitor emission control devices on their vehicles. In addition to monitoring smog equipment, manufacturers began to use the on-board diagnostic system to monitor various aspects of the engine, transmission, and chassis. While many car manufacturers were playing catch-up in the mid-nineties to implement their OBD-II operating system, most V6 Mustangs starting in 1994 were equipped with the second generation on-board diagnostics system (OBD-II). The OBD-II system is much more advanced than its predecessor and is able to monitor many different aspects of the vehicle to ensure proper operation. In turn, hundreds of fault codes are available to give owners and technicians a starting point on where to look if a problem in the vehicle arises. Illumination of the malfunction indicator lamp (MIL), also referred to as a check engine light (CEL), indicates a fault somewhere in the vehicle. A generic OBD-II scanner can retrieve the code and provide the first step towards curing the problem. This article will show how to retrieve a diagnostic trouble code, as well as outline several common fault codes in the 1994 to 2004 V6 Mustang models.
Potřebný materiál
- OBD-II code reader or scan tool
Read Diagnostic Trouble Code
If a check engine light has illuminated on the dash, a fault code is stored in the computer and can be retrieved with an OBD-II code reader.
- Using a generic OBD-II code reader, plug the reader into the diagnostic port located under the dash on the driver’s side.
- With the code reader plugged in, turn on the ignition. It is not necessary to start the car.
- Scan for codes.
- Fault codes are composed of a letter that precedes four digits. Depending on the make and model of your code reader or scan tool, you may be able to view additional information such as freeze frame data associated with the fault code.
- Upon repairing the faulty component, stored fault codes can be cleared to reset the check engine light.
For an entire list of OBD-II fault codes, see the related discussion: OBD-II Trouble Codes.
Pro Tip
If you do not have a code reader, many auto parts stores will scan fault codes for free.
Listed below are several common fault codes and their underlying issues for V6 Mustang models.
Oxygen Sensor Codes
The most common issue typically associated with a check engine light is found within the oxygen sensors and related components. The oxygen sensors monitor exhaust gases to determine the correct air-fuel mixture, as well as monitor the efficiency of the catalytic converter(s). While it is very common for oxygen sensors to fail and simply need replacing, the source of the problem can originate upstream of the sensors.
- Oxygen sensor operation can typically be tested by measuring its voltage outputs with a digital multimeter as the engine warms up. Measurments that fall outside of the factory specifications will require replacement sensor(s) to be installed.
A functioning oxygen sensor can trip a check engine light if the gases it is measuring are not within spec. Possible causes include:
- Vadné vstřikovače paliva
- Vadný snímač hmotnostního průtoku vzduchu
- Bad ignition coil or spark plus (misfires)
- Netěsnosti výfuku
- Netěsnosti vakua
- Faulty wiring at oxygen sensors
Pro Tip
An oxygen sensor fault code accompanied by an upstream fault code (i.e. misfires, fuel injectors, etc.) is usually the cause of the O2 sensor fault, and should be corrected before assuming the O2 sensor is bad.
Kódy vynechávání zapalování motoru
Perhaps one of the more common fault codes to pop up on the V6 Mustang models are misfire codes. Misfire codes begin with P030*, with the last digit indicating which cylinder is experiencing the misfire. It is not uncommon to have multiple misfire codes for various cylinders stored in the fault memory. A misfire is when the air-fuel mixture in a particular cylinder does not combust to produce power. Misfires will leave your engine running rough and lacking power. Causes for a misfire code include:
- Faulty ignition coil (coil pack)
- Špatné zapalovací svíčky
- Loose, disconnected, or aging spark plug wires
- Špatná kvalita paliva
- Ucpaný palivový filtr
- Vadné palivové čerpadlo
- Ucpaný vstřikovač paliva
Pro Tip
It is best to start with the simplest of fixes that are easy to access and work your way up to the more difficult to replace components. This will often save time and money, as a simple fix can cure major driveability issues.
Evaporative Emission System Codes
The evaporative emissions system is in place to collect fuel vapors from the fuel tank and fuel system from venting to the atmosphere. These fumes are typically collected in the charcoal canister and eventually burned during normal engine combustion. While a fault code associated with the evaporative emissions system may seem overwhelming, something as simple as a faulty gas cap can be the cause of your check engine light. In fact, Ford issued a technical service bulletin in 2003 identifying a loose, leaky, or faulty gas cap as the culprit behind many of the Mustang evap fault codes. Evaporative emission fault codes are typically caused by:
- Bad gas cap
- Deteriorated gas cap seal
- Leaking fuel tank filler neck
- Small/large leak in fuel vapor hose(s)
- Špatný odvzdušňovací ventil
- Únik palivové nádrže
Coolant Temperature Codes
Fault codes associated with the coolant temperature or coolant temperature sensor can cause a host of issues on the Mustang V6. A fault code ranging from P0115 to P0119 indicates that the PCM is reading abnormal values at the coolant temperature sensor. A failed or failing coolant temperature sensor may cause the temperature gauge to wildly fluctuate and the electric fan to operate intermittently. Additionally, the engine may run poorly and see a reduction in fuel economy. Similar to an O2 sensor, the temperature sensor can be tested with a digital multimeter to check its operation. Many times, if there are no signs of engine overheating, the temperature sensor has failed and should be replaced. That being said, the following issues may cause a temperature related fault code:
- Nízká hladina chladicí kapaliny
- Selhal termostat
- Inoperable cooling fan
- Plugged radiator/cooling system
- Selhávající vodní čerpadlo
Pro Tip
A quality shop service manual for your specific vehicle can go a long way in troubleshooting diagnostic fault codes. Manuals from companies like Chilton and Haynes include troubleshooting guides that are typically available at most auto parts stores.
Související diskuse
- OBD II Trouble Codes — MustangForums.com
- Help With Mustang Codes — MustangForums.com
- P0301 Error Code 2002 V6 — MustangForums.com
i realized that there isnt a dedicated thread (and possible sticky :winks) on how to pull codes. i checked the 2.3 and the 5.0 tech sections and didnt find any. so i’m gonna give it a try, and everyone please help/correct/add to this. (to the moderator, if this is good enough, can i post it over in the 5.0 and v6 sections to help them out too since the procedure is the same? i ask because i know the rules about double posting lol.)
i am not knocking anyone who asks about how to pull codes, but i think it would be advantageous for everyone if there was a dedicated thread we could link to, rather than having to type out the procedure over and over and risking accidentally leaving something out.
if theres something wrong with your mustang the first thing you should do is pull the codes! even the abcence of codes gives us usefull information to go on to help you find out what the problem is and get your mustang back on the road. even if youre not currently having a problem, its a good idea to pull codes on a frequent basis (minimum every 2 weeks, but no longer than once a month) so you can know how well, or not, your car is running, and also catch a problem when its small before it leaves you stranded on the side of the road.
i am just going to go over some key points that people who are new to these cars might not know or might miss. there are plenty of good writeups already done in the links i’m going to list at the end, and i dont see a need to reinvent the wheel on this.
there are two ways to go to obtain codes: with a code reader, and without. as of this writing code readers are $25-30 at all the major autoparts stores. the code reader has the advantage of being easier for some to use (vs the non code methods) and also easier to interpret the codes themselves. the non code methods are cheaper, since they cost a couple bucks if you dont already have the materials on hand. they can also be a bit less user friendly (especially the first few times), and it can be difficult to count the codes correctly. i would recommend that you try to use a non-code reader method to see if it works for you, and if it is too frustrating or innacurate then you can buy a code reader and not feel like you wasted money. for your first attempt, i would highly advise having a helper as well as recording the entire test. that way if youre having trouble deciphering the flashes you can review the vid or post it and get online help.
your mustang can be making trouble codes without your check engine light (cel for short) being on. just because the light isnt on doesnt mean that there arent codes in the cars computer (called the mcu or eec-iv depending on your model year). the plugs you need to get at are on the driverside behind the tower. see the pic below for a visual. with the mcu, you will only find the large plug since it doesnt have the smaller one. if youre having trouble finding them, start tracing the wiring harness and you should eventually come across them.
when doing an engine off test, make sure you wait for both code groups. there are two groups of codes that will be output; active and intermittant, and both batches will repeat.
active specifically means problems that are happening at the time of the test. if you have a problem that disapears and reappears it will only be listed in the first active code group if it is happening during the test. it will however be making codes that will be output in the second batch of intermittant codes.
about 5-10 seconds after the active codes repeat the intermittant codes will begin. these are codes for problems that arent happening during the test, but the eec/mcu has noticed them as being problems at various times in the recent past. if i remember correctly, it takes 40 start and run cycles for these codes to clear. again, these codes will repeat.
for both engine off and engine running tests you will always at least get a code 11 or 111 which means system pass and all is good. 1991 and newer will output 3 digit codes, everything older is two digit.
for engine running tests, make sure the car is at normal operating temperature! it is very important that certain components like the o2 sensors be heated up during this test, since the eec/mcu is checking them for proper operation. there are various procedures depending on model year that you must do to the car either before or during the test to get accurate results, so pay very close attention to what is listed for your model year and engine size.
if your mustang wont at all start, then at least do the engine off test to give everyone some info we can troubleshoot off of. but if at all possible run that engine around the block, or at least keep it idleing for a good 10 min to warm it.
the first code you will always get will be an engine id code. the id code flashes are always half the number of cylinders you have. 2 flashes=4 cylinder, 3=v6, 4=v8.
after that, and after doing any applicable actions the directions call for for your model year and engine size, the codes will be output. again, they will repeat.
on engines with sequential fuel injection (sefi) you can even do a cylinder balance test after doing the above two tests. in my experience its very accurate. personally i recommend you repeat this test a minimun of twice, but 3-4 times is prefferable if youre using it to diagnose a problem. generally its not necessary to do this test the first time youre scanning for codes to diagnose a problem, since problems rarely lead down this road. but be aware that the members helping you figure out where the devil in your car is might tell you to do the test to get the info necessary to diagnose your problem.
here are some great links. i will specify under each one what it covers.
http://www.troublecodes.net/Ford/
this is a very good set of instructions on how to pull codes without using a code reader. even if you have a reader, it doesnt hurt to read thru.
http://www.equus.com/Content/Support/Manual/3145_FDCR_(E)_20NOV2002.pdf
this link is absolutely excellent for the procedures to pull codes. its written for use with a code reader, but you can easily use it with any of the non-reader methods.
DIY KOEO/KOER/Cylinder Balance Self-Test Procedure
very good write up on how to pull codes using a volt meter, as well as the jumper wire method.
http://www.merkurencyclopedia.com/EEC-IV/EECTEC10.PDF
this one has a very good technical breakdown of both the mcu and eec-iv processors, as well as instructions on how to do a maf conversion, and also has a table for identifying which speciffic eec/mcu you have.
Fuel Injection Technical Library » EEC Program Codes
this has another table for how to identify your eec. very good if youre trying to figure out which stock computer is supposed to go with your engine. on the side of the page are links for how to do a self test, as well as lists for finding out what the codes you get actually mean. there are also instructions on various other procedures, so take a good look at this site.
EEC IV(91-93) For NOOBS
this one has some very detailed info and great diagrams of the eec-iv and its related wiring. good for when your mustangs problem falls under the heading of «the devil is in the details»
Ford EEC — Wikipedia, the free encyclopedia
some good general info about the eec processors. sorry mcu guys, but i havent been able to find anything for you.
