Repair Topics / Check
Engine Light-1 / Check Engine Light-2 /
Check Engine Light-3 / Check
Engine Light-4Car Service Engine Soon or Check Engine Light On or Flashing
Introduction
If you see a "check engine" or a "service engine soon" light
in your instrument cluster; your car has stored a
diagnostic trouble code.
Which
means the computer system on your vehicle has detected a problem within various
systems it controls. Your car has many different sensors that monitor the various
vehicle systems. If the check engine light has been illuminated your vehicle enters
into "limp mode" this means it is running on a predetermined program that
can cause
poor mileage, increased emissions and low engine power output. An engine
trouble code reader is an easy to
use tool to use. All 1996 and newer vehicles utilize a "D" style plug
that is called a DLC (data link connector). This connector is used to
connect to the
code reader.
Check Engine or Service Engine Soon Light
There are two modes of check engine light illumination, the first is the
light will come on for a short time then go off. This mode means there is a
problem that is considered "minor". The next mode is the light stays on
continuously. This means a minor problem has been allowed to continue for an
extended amount of time or the problem is more serious and needs attention
sooner than later. Most check engine light locations are somewhere in the
instrument cluster panel in a place that is easily visible.
Most vehicles connector is located in the driver's compartment near the
bottom of the dash. Once the
code reader is plugged in you can retrieve the trouble code the PCM (powertrain
control Module) has
stored in its memory. These codes are the same codes the dealer and repair shops
will use to diagnose and repair your vehicle, as well as clearing the trouble codes
from the computers memory after the repair have been made.
The check engine or service engine soon light holds the same meaning.
Different manufacturers call this problem detection mode various things, but
"check engine" or "service engine soon" covers most of them.
This computer monitoring system has built in fail safes. What this means
is a problem must be seem by the computer more than once and for an extended
amount of time. If the computer detects a problem once and then not again
the check engine light will not come on. The failure must be repetitive and
within a certain time frame.
Some simple conditions for the check engine light to come on is leaving
the gas cap off after refueling. The system is designed to hold the fuel
tank to a slight vacuum. If the the system cannot hold vacuum it will
illuminate the check engine light until the gas cap is reinstalled.
Service Engine Soon Light Scan for Trouble Codes Video
Locate Your Vehicle's Computer Connector
Data Link Connector
Locate your vehicle's computer connector (DLC), most are on the lower
driver's side. In some vehicles you might need to look around a little, on the
passenger's side, and around the center console under a plastic cover.
Connecting to The Computer to Read Codes
Simple Trouble Code Reader
Connect your code reader to the under dash connector. The code reader will automatically
turn on and prompt you to the next step for code retrieval. Once the code has been
identified look up the identification on the trouble code chart supplied with your
code reader. After repair has been made clear trouble codes and recheck system.
After codes have been cleared the computer system is ready for internal testing,
this means that while the car or truck is in operation the onboard computer is performing
tests. These tests are called "monitors" most cars have between 4 and 8 monitor
systems. The computer goes through its testing procedure in about 40 to 60 miles.
Common Problems
- OBD2 (OBDII) Scan Test is Incomplete - The computer system or PCM ( powertrain control module) that controls your car is equipped
with a basic operating program. This operating program is designed to control
your engine, transmission, emissions, safety systems and more. If a scan has
been performed by using a
code scanner
and a "scan could not be completed" code is retrieved further troubleshooting
is necessary. Usually a trouble
code P1000 or manufacturers equivalent. Below is listed several reasons
for this condition.
Stuck Engine Thermostat
- If the engine thermostat has stuck open it forces the engine coolant to
stay at too low of a temperature causing the PCM to
stay in open loop. This open loop creates a state of preprogrammed
parameters were no diagnostic tests can be preformed. (the PCM is
continuously waiting for the engine to heat up to operating temperature).
Shorted
Oxygen Sensor/Coolant Temperature Sensor - The ECM/PCM
relies on information from main sensors to operate,
if one of these sensors is severely shorted it can cause the ECM/PCM to stay
in open loop causing an incomplete systems check.
Shorted
Fuel Injector -If a fuel injector
short circuits it can cause the engine not to run by shorting the injector
driver in the ECM/PCM. This
in turn can cause incomplete code gathering which will result in a P1000
code.
- After a car repair has been performed the MIL indicator will illuminate
because the technician neglected to plug in a sensor.
- A blown fuse can cause the MIL to illuminate.
- A shorted sensor can cause the MIL to illuminate.
Check Engine Light Questions
Question: 1997
Grand Voyager 3.3 Liter mileage: 158,000. Service Engine Soon Light stays ON.
Had 1 of the O2 Sensors replaced according to Repair Shop Code Scan. Light went
out but came back ON and remains ON. Need to pass NYS Emissions Test soon. Are
these Minivans noted for Service Engine Soon Lights? What can I do to put this
light out to pass the emissions test? Thank you.
Answer: The computer code for the oxygen sensor may
be caused by a lean fuel mixture not a faulty oxygen sensor. Check the fuel
supply particularly the fuel filter and pump. Also, check the mass airflow sensor
and check the engine intake system and hoses for vacuum leaks.
Question: 1999 Ford Explorer 4.0. Code 12, Rpm not within self test upper
limit and code 14, profile ignition pick-up circuit fault. It is a distributor-less
system. I have replaced the PCM, ICM module, TPS, EGR valve, spark plugs and
wires, the EGR sensors test good. I'm at a loss as where to go to correct these
two faults.
Answer: Try replacing the pickup coil and the ignition coil.
Question: 2001 Mazda Millennia mileage: 72,000. Yesterday, I got
a check engine light. The local AutoZone diagnosed the P0173 code to be "fuel
trim". They couldn't elaborate on what that might mean. I just bought the car
and to my knowledge the injectors haven't been cleaned. I did have to replace
an O2 sensor a month ago. I just read on the web that some cars require a mechanic
to disconnect the battery when changing the O2 sensor to reset the long term
fuel trim. I remember having to reset the radio after their work. Is it the
injectors? What am I missing?
Answer: The code you mentioned is a general code for problems
with the fuel injection system. It could mean that the fuel pressure regulator
is faulty, or something is wrong with the fuel pump or the fuel injectors.
Question: 1989 Toyota Tercel 4 cyl mileage: 91,000. Dear
Bob and Ken: My problem concerns my 1999 Toyota Tercel, 91000 miles, 4-speed
manual transmission, most recent oil change was about 1800 miles ago, and no
major repairs since purchasing the car at 40000 miles. I recently
made a 1600-mile trip from Virginia to Colorado; I had the oil changed, fluids
topped-off, and air filter replaced. Additionally, I had an emissions
inspection done a few weeks before, and the results were excellent. Approximately
half way through the trip and some very bumpy interstate driving in Arkansas
and Oklahoma, my "Engine" light came on. I pulled over immediately to
check under the engine, checked the oil level, belts, hoses, etc. and found
no noticeable irregularities, except that the overflow container for the radiator
fluid was empty. There was still plenty of fluid in the radiator itself,
but I replaced the fluid/water mixture anyway. I noticed no odd smells
or drivability difficulties, so I continued driving. I stopped overnight
and the following morning, I checked my owner’s manual and it said that this
light comes on due to a problem with the engine's electrical system. Being
that the roads were rough, I suspected maybe a fuse had been knocked out, so
I removed, inspected, then replaced all of the fuses. I started the car
and the engine light was off. I continued driving, but after about 6 hours
of interstate driving (70-80 mph) the light came on again. Still,
I did not notice any smells, sounds, or drivability problems. I continued
to drive as I was in the middle of nowhere and arrived in Colorado, still with
the engine light on. I spoke with a technician about this before and his
recommendation was that the oxygen sensor could be the problem. I have
researched the function and possible problems of the O2 sensor and it seems
like if that were the culprit, my exhaust would smell like "rotten eggs" OR
produce a black smoke (depending on lean or rich mixture). Is this correct?
Or could the sensor be malfunctioning WITHOUT a real problem with the mixture?
What type of problems could develop with continued driving? Could there
be another cause to the engine light coming on? Is there some way
to check the sensor myself without having to take to a mechanic? Could
the missing radiator fluid have caused something to go wrong (I have noticed
no leaks in the overflow tank since)? Could the change in altitude cause
something? I apologize for the length of this, but wanted to make sure
to get all of the information here. Thank you in advance for your help!
Answer: You probably do have a faulty oxygen sensor. With
91000 miles on your car, it would be good practice to replace it anyway.
If your problem persists, then scan the computer for fault codes.
Oxygen sensors go out of range at times, but still work.
Question: 1994 Honda Civic mileage: 187,000. Check engine
light continues to come on periodically. When the light is on the overdrive
doesn't engage. I tested the car with light on and off. I replaced
the oxygen sensor, fuel filter and had it checked by a mechanics computer code
system. The trouble code 1 (oxygen content) circuit continues even though
I have done all the Haynes manual suggests. I called the dealer and they
are stumped also. The only thing I can think of next is the Engine control
module, however that part is $1250. Car runs excellent with the light
on or off. What do you think is the next step?
Answer: Check the air diverter valve that puts fresh air into
the exhaust system, as it may not be functioning properly.
Question: 1992 Ford Taurus Station Wagon mileage: 130,000.
My mechanic doesn't seem to know what the problem is with my car so I have come
to ask you. The engine light keeps coming on. It doesn't stay on long
enough to register on the computer. Maybe 10 seconds at most.
Some time it just barely flashes. It will go off if I accelerate, brake,
or just wait. The engine does seem bogged down sometimes when the light
is on, but not all the time. Another thing, (I don't know if this is related
or not) sometimes the signal lights don't work. I can go for months where
it is fine then a day or a week where they don't work. The heater also
doesn't work if the signal lights are not working. I know those two things
are related, but the engine light might have nothing to do with them.
Please help! If there is, more information that you need just let
me know. Thank you! Jessica
Answer: The “check engine” light will “light” when there is a
malfunction in the engine management system. The fault code is then stored
in the computer. The computer must be scanned to retrieve these stored
faults to pinpoint the malfunctioning component. Also, take a 12-volt
test light and check out the power to the heater and turn signals when they
are not working.
Question: 1996 Plymouth Grand Voyager 3.0 mileage: 177,000.
Bob and Ken, Great web site. First time caller. Quick question.
A few thousand miles back 75 or 80K the maintenance required light on the dashboard
illuminated. My local mechanic said that Plymouth set those to go off
based upon mileage on this particular vehicle. He reset the light.
Guess what? It comes back on again recently. Stupid me did not ask
for the reset steps. What are the procedures to reset that light?
I hate to go buy a $50 manual for a van I plan to sell in a couple of months.
Or, worse yet, pay a Plymouth dealer $200 to put the light out. BY the
way, the van does not have any problems at all. Gas mileage is still in
the upper 20s in the city and in the mid 30s on the highway. Oh yea the
transmission was changed out (standard for these vans) at 88K. Thanks
for the tip. Pat
Answer: However, the “check engine” light will “light” when there
is a malfunction in the engine management system. The fault code is then
stored in the computer. The computer must be scanned to retrieve these
stored faults to pinpoint the malfunctioning component. Because the check
engine light indicates something is wrong, a trip to you neighborhood automobile
service center sooner rather than later is recommended.
Question: 1993 Isuzu Trooper 3.2 mileage: 97,000. My service
engine light was always coming on but nothing appeared wrong with the vehicle.
My gas pump and oxygen sensor had just been replaced, my oil changed and my
charging system checked. My mechanic said that it appeared that
I needed to replace my modulator but rigged it so it would work okay for a while.
Will this hurt the vehicle? How important is this modulator?
Answer: Your car is equipped with a computer controlled
engine management system. An independent auto service center can scan
your computer for fault or error codes. The information should pinpoint
the malfunctioning components. If a major tune-up has not been done
recently, this could be the cause of your problem. Replace the spark plugs,
plug wires, fuel and air filters, etc. Also, replace the oxygen sensor.
In addition, service the fuel injection system. Clean the carbon deposits
from the throttle bore and idle passages.
Question: 1998 Chevrolet Lumina mileage: 85,000.
If the car is warmed up and I'm at highway speed, then suddenly let off the
gas, the service engine soon indicator will light. It is generating an
EGR code (32, I believe). The light generally stays on until I shut off
the engine. This happens more often when the outside temperature is at
least roughly 40 degrees. However, this does not have a big effect.
I have taken the digital EGR valve off and none of the valves is sticking.
Answer: Your EGR valve may not be operating properly and
may need replacement.
Question: 1989 Jeep Cherokee Sport ST 6 mileage: 83,000. On a trip
check, engine light came on 40 miles into trip. I pulled off and checked
fluids, all ok. Vehicle cooled down, all gauges looked ok. Continue
trip, another 40 miles motor acts as if it will cut off. Pull off once
again, let cool down. Vehicle starts immediately. Runs perfect for
another 40 miles, does same thing. I notice that I cannot set cruise control.
I have replaced fuel filter, spark plugs, plug wires, distributor cap, rotor
button, and ignition coil. Still have problem. Next move is EGR valve. Call Jeep shop to order part, they say I haven't an EGR valve
in their books, must be something else? Take to shop, they read codes,
nothing out of the ordinary, all sensors are performing correctly.
They cannot recreate problem. They return to me unrepaired and still can
not set cruise control. What gives? EGR or oxygen sensors?
I would gratefully appreciate any insight you may have on my problem.
Thank you.
Answer: The “check engine” light will “light” when
there is a malfunction in the engine management system. The fault code
is then stored in the computer. The computer must be scanned to retrieve
these stored faults to pinpoint the malfunctioning component. Because
the check engine light indicates something is wrong, a trip to you neighborhood
automobile service center sooner rather than later is recommended. Try
another service center; the first one appears it have missed it.
Question: 1989 Mercury Sable mileage: 89,000. The service engine
light is on, had it checked and got a code 41-oxygen sensor. Need to know
if it is the front or back that needs to be replaced. Or if I should replace
both. Thank you.
Answer: Replace both Oxygen sensors. You may have
to have your computer scanned again to reset the light.
Question: 1990 Plymouth Voyager mileage: 183,000. Just replaced
the 02 sensor, but we are unable to turn off the maintenance-required light.
Any suggestions?
Answer: Try disconnecting the negative battery for
approximately 15 seconds and reconnecting. If the light is still on, have
the engine computer scanned for fault codes.
Question: 1989 Dodge Grand Caravan 3.3 mileage: 72,000.
I read the questions for Tuesday on the dodge caravan. My check
engine light also comes on. What I want to know, if you can be more specific,
in your opinion, what are the possibilities that can make your engine light
come on. I have taken my car to mechanics, and they tell me everything
that is wrong with my car that really isn't. It's hard to find an honest mechanic.
I want to make sure I know what they are talking about, and that they are not
lying to me.
Answer: There are a number of things that can malfunction
and cause the check engine light to come on. We are sorry to hear you
are getting the run-a-round with your car repairs. Talk with friends and
neighbors to locate a professional auto mechanic you can trust. Have him/her
inspect the car giving him/her the same information you gave us.
Question: 1989 Mitsubishi Lancer mileage: 70,900. This morning,
my check engine light came on and stayed on. I don't know what's wrong
with it. This is my first car. I tried to take it to a repair shop,
but was told to take it to a Mitsubishi dealership. Do dealerships fix
cars also or should I just take it to a different repair shop?
Answer: Try a different repair shop that has the proper
equipment. The “check engine” light will “light” when there is a malfunction
in the engine management system. The fault code is then stored in the
computer. The computer must be scanned to retrieve these stored faults
to pinpoint the malfunctioning component. Because the check engine
light indicates something is wrong, a trip to you neighborhood automobile service
center sooner rather than later is recommended.
MORE: Check engine or
service engine soon light questions
Repair Topics / Check
Engine Light-1 / Check Engine Light-2 /
Check Engine Light-3 / Check
Engine Light-4
Related Subjects
