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COOLANT SENSOR. Usually located on the cylinder head or intake manifold, this sensor is used to monitor the temperature of the engineís coolant. Its resistance changes in proportion to coolant temperature. Input from the coolant sensor tells the computer when the engine is warm so the PCM can go into closed loop feedback fuel control and handle other emission functions (EGR, canister purge, etc.) that may be temperature dependent.
Coolant Sensor Strategies: The coolant sensor is a pretty reliable sensor, but if it fails it can prevent the engine control system from going into closed loop. This will result in a rich fuel mixture, excessive fuel consumption and elevated carbon monoxide (CO) emissions - which may cause the vehicle to fail an emissions test.
A bad sensor can be diagnosed by measuring its resistance and watching for a change as the engine warms up. No change, or an open or closed reading would indicate a bad sensor.
OXYGEN (O2) SENSOR. Used on both carbureted and fuel injected engines since 1981, the oxygen (O2) sensor is the key sensor in the fuel mixture feedback control loop.
Mounted in the exhaust manifold, the O2 sensor monitors the amount of unburned oxygen in the exhaust. On many V6 and V8 engines, there are two such sensors (one for each bank of cylinders).
The O2 sensor generates a voltage signal that is proportional to the amount of unburned oxygen in the exhaust. When the fuel mixture is rich, most of the oxygen is consumed during combustion so there is little unburned oxygen in the exhaust. The difference in oxygen levels between the exhaust inside the manifold and the air outside creates an electrical potential across the sensorís platinum and zirconium tip. This causes the sensor to generate a voltage signal. The sensorís output is high (up to 0.9v) when the fuel mixture is rich (low oxygen), and low (down to 0.1v) when the mixture is lean (high oxygen).
The sensorís output is monitored by the computer and is used to rebalance the fuel mixture for lowest emissions. When the sensor reads "lean" the PCM increases the on-time of the injectors to make the fuel mixture go rich. Conversely, when the sensor reads "rich" the PCM shortens the on-time of the injectors to make the fuel mixture go lean. This causes a rapid back-and-forth switching from rich to lean and back again as the engine is running. These even waves result in an "average" mixture that is almost perfectly balanced for clean combustion. The switching rate is slowest in older feedback carburetors, faster is throttle body injection systems and fastest in multiport sequential fuel injection.
If the O2 sensorís output is monitored on an oscilloscope, it will produce a zigzagging line that dances back and forth from rich to lean. Take a look at the waveform on the opposite page - thatís what a technician wants to see when he checks the O2 - think of it as a kind of heart monitor for the engineís air/fuel mixture.
O2 Sensor Strategies: Unheated one- or two-wire O2 sensors on 1976 through early 1990s applications should be replaced every 30,000 to 50,000 miles to assure reliable performance. Heated 3 and 4-wire O2 sensors on mid-1980s through mid-1990s applications should be changed every 60,000 miles. On OBD II equipped vehicles, the recommended replacement interval is 100,000 miles. The O2 sensorís responsiveness and voltage output can diminish with age and exposure to certain contaminants in the exhaust such as lead, sulfur, silicone (coolant leaks) and phosphorus (oil burning). If the sensor becomes contaminated, it may not respond very quickly to changes in the air/fuel mixture causing a lag in the PCMís ability to control the air/fuel mixture.
The sensorís voltage output may decline giving a lower than normal reading. This may cause the PCM to react as if the fuel mixture were leaner than it really is resulting in an overly rich fuel mixture.
How common is this problem? One EPA study found that 70 percent of the vehicles that failed an I/M 240 emissions test needed a new O2 sensor.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR. This sensor is mounted on or connected to the intake manifold to monitor intake vacuum. It changes voltage or frequency as manifold pressure changes. The computer uses this information to measure engine load so ignition timing can be advanced and retarded as needed. It performs essentially the same job as the vacuum advance diaphragm on an old fashioned mechanical distributor.
On engines with a "speed density" type of fuel injection, the MAP sensor also helps the PCM estimate airflow. Problems here may cause an intermittent check engine light (light comes on when accelerating or when the engine is under load), hesitation when accelerating, elevated emissions and poor engine performance. The engine will run with a bad MAP sensor, but it will run poorly. Some PCMs can substitute "estimated data" for a missing or out of range MAP signal, but engine performance will be drastically reduced.
MAP Sensor Strategies: Some MAP sensor problems are not the fault of the sensor itself. If the vacuum hose that connects the MAP sensor to the intake manifold is loose, leaking or plugged, the sensor canít produce an accurate signal. Also, if there is a problem within the engine itself that causes intake vacuum to be lower than normal (such as a vacuum leak, EGR valve thatís stuck open or leaky PCV hose), the MAP sensorís readings may be lower than normal.
THROTTLE POSITION SENSOR. Mounted on the throttle shaft of the carburetor or throttle body, the throttle position sensor (TPS) changes resistance as the throttle opens and closes. The computer uses this information to monitor engine load, acceleration, deceleration and when the engine is at idle or wide open throttle. The sensorís signal is used by the PCM to enrich the fuel mixture during acceleration, and to retard and advance ignition timing.
Throttle Position Sensor Strategies: Many TPS sensors require an initial voltage adjustment when installed. This adjustment is critical for accurate operation. On some engines, a separate idle switch and/or wide open throttle (WOT) switch may also be used. Driveability symptoms due to a bad TPS can be similar to those caused by a bad MAP sensor: The engine will run without this input, but it will run poorly.
MASS AIRFLOW SENSOR (MAF). Mounted ahead of the throttle body on multiport fuel injected engines, this sensor monitors the volume of air entering the engine. The sensor uses either a hot wire or heated filament to measure both airflow and air density.
MAF Sensor Strategies: The sensing element in MAF sensors can be easily contaminated causing hard starting, rough idle, hesitation and stalling problems.
VANE AIRFLOW SENSOR (VAF). The VAF has a mechanical flap-style sensor that is used on Bosch and other import multiport fuel injected engines. The function is the same as a mass airflow sensor, but air pushing against a spring-loaded flap moves a rheostat to generate an electronic signal.
VAF Sensor Strategies: The drivability symptoms for the VAF are the same as those of a mass airflow sensor if the sensor fails.
MANIFOLD AIR TEMPERATURE (MAT) SENSOR. Mounted on the intake manifold, this sensor changes resistance to monitor incoming air temperature. The sensorís input is used to adjust the fuel mixture for changes in air density.
MAT Sensor Strategies: Problems with the manifold air temp sensor can affect the air/fuel mixture, causing the engine to run rich or lean.
CRANKSHAFT POSITION SENSOR. Used on engines with distributorless ignition systems, the crankshaft position sensor serves essentially the same purpose as the ignition pickup and trigger wheel in an electronic distributor. It generates a signal that the PCM needs to determine the position of the crankshaft and the number-one cylinder. This information is necessary to control ignition timing and the operation of the fuel injectors. The signal from the crank sensor also tells the PCM how fast the engine is running (engine rpm) so ignition timing can be advanced or retarded as needed. On some engines, a separate camshaft position sensor is also used to help the PCM determine the correct firing order. The engine will not run without this sensorís input.
There are two basic types of crankshaft position sensors: magnetic and Hall effect. The magnetic type uses a magnet to sense notches in the crankshaft or harmonic balancer. As the notch passes underneath, it causes a change in the magnetic field that produces an alternating current signal.
The frequency of the signal gives the PCM the information it needs to control timing. The Hall effect type of crank sensor uses notches or shutter blades on the crank, cam gear or balancer to disrupt a magnetic field in the Hall effect sensor window. This causes the sensor to switch on and off, producing a digital signal that the PCM reads to determine crank position and speed.
Crank Position Sensor Strategies: If a crank position sensor fails, the engine will die. The engine may, however, still crank but it wonít start. Most problems can be traced to faults in the sensorís wiring harness. A disruption of the sensor supply voltage (Hall effect types), ground or return circuits can cause a loss of the all-important timing signal.
KNOCK SENSOR. The knock sensor detects engine vibrations that indicate detonation is occurring so the computer can momentarily retard timing. Some engines have two knock sensors.
Knock Sensor Strategies: A failure with the knock sensor can cause spark knock and engine damaging detonation because the PCM wonít know to retard ignition timing if knock is occurring.
BAROMETRIC PRESSURE (BARO) SENSOR. The baro sensor measures barometric pressure so the computer can compensate for changes in altitude and/or barometric pressure that would affect the fuel mixture or timing. Some MAP sensors also perform this function.
VEHICLE SPEED SENSOR (VSS). The vehicle speed sensor, or VSS, monitors vehicle speed so the computer can regulate torque converter clutch lockup, shifting, etc. The sensor may be located on the transmission, differential, transaxle or speedometer head.
Vehicle Speed Sensor Strategies: A problem with the vehicle speed sensor can disable the cruise-control system as well as affect transmission shifting and converter engagement.
Replacing a sensor wonít solve a drivability or emissions problem if the problem isnít the sensor. Common conditions such as fouled spark plugs, bad plug wires, a weak ignition coil, a leaky EGR valve, vacuum leaks, low compression, dirty injectors, low fuel pressure or even low charging voltage can all cause driveability symptoms that may be blamed on a bad sensor. If thereís are no sensor-specific fault codes, these kinds of possibilities should be ruled out before much time is spent on electronic diagnosis.
My VOLVO S40 with mileage of about 122,000 km, engine and transmission models were B4204S, MPS6. The car water temperature suddenly down during driving.Connect the VIDA DICE to read the relevant fault codes, just only one: "ECM-0118 engine coolant temperature sensor, signal is too high, B420S3 0". How can i do? Anyone can help me?
Bought my s40 5 months ago had a clean carfax report and started great. 3 weeks ago I had trouble starting and its been everyday since, car has trouble cranking over it takes about 10 seconds. Once car is started it can start right up within a 30 minute period. I found it starts better in cold weather. Scanned codes 3 times me and mechanic found nothing. Just replaced plugs and coils still no luck. Sorry for bad English.
Hello i have a problem with my 2003 s-40 today i try to start it but i notice that ignition key wont go all the way to ignition position i try few times and once the key wont come out it was like stuck in there i move gear selector just in case it was on other than park and it wasnt and still wont turn all the way , it looks like when you miss the start and need to try again that you have to take the key all the way back to off or it Will not go to start position , well i try this many times and key still dont go To start PLEASE HELP
I just open the lover cover remove the scree from the electrical part of the switch and move the center of it where the mechanical end fit and My car start it looks like the key cylinder is stuck inside not letting turn all the way
Hello I have a 2003 s-40 with a automatic transmission and the problem is that every time I slow down transmission kick so hard when it does the change gear down , I check on engine mounts and replace 2 that was bad , the rear lower and the one is over the transmisson under the air cleaner , it reduce the problem a little but still kicking , basicly the only engine mount that I didnt check is The one by the timing belt , that dealer ship told me that one is hidraulic but dont know how to check on it, please any ideas
I have a 2002 s40 1.9 turbo over the past 2 weeks car overheats on hot days when ac is turned on at that time no engine light was on. I flushed the system put fresh fluids in changed thermostate and ect sensor drove it around and still same problem checked fluid level and that was good. A couple days later engine light came on and code says below temp checked fluid again still good car still overheats when ac is on outside temps here are mid 80s does not overheat in the mornings its been chilly out. I drive 90 highway miles a day for work. Any ideas would be great really do not want to take it to dealership. Also as of today the heater ac fan is not blowing any heat or ac out of vents I can hear the ac working just not blowing.
Our 2000 V40 suffered a complete loss of coolant while at a light, and subsequently froze up due to the heat. Later we refilled it with hot water and were able to get it about a mile home. It was towed to a shop where they replaced the radiator and a hose but the tech tells me that likely due to a warped head or damaged gasket, it is now pressurizing the cooling system and needs attention before being driven for any length of time. He did indicate that these heads are either hard or impossible to resurface, due to the turbo and increased compression ratio, so that leaves the installation of a new or used good head, way more expensive than the car is worth.
But it starts right up, doesn't run rough at first, seems and sounds like it did before the event, so we're cautiously optimistic at this point.
Since we had no other feasible option to repair it, I investigated the various "Bar's Leaks" products and discovered that apparently there are quite a few folks out there who say they have successfully used the Bar's Leaks "Permanent" Head Gasket Fix product. This is a liquid containing a blend of sodium silicate and variously-sized flakes of what appears to be copper, all of which supposedly works its way in whatever little nooks or crannies causing a leak of water or combustion gas, and then it becomes fused in place due to the intense pressure and heat.
I could believe that. In fact, I bought it hook, line, and sinker.
So I put in a can according to directions. Now we're trying really hard to prove that the pressure buildup we see after running the engine for a few minutes is normal and due only to heating of the water which naturally increases the pressure.
The tech said we should try this test - Remove the reservoir filler cap to equalize pressure, then replace it. Start the car, idle for 15 seconds, then run at 2500 for another 15 seconds, and turn off. Now, very slowly twist off the cap and listen to whatever sound comes out from whatever pressure was generated.
We did that and we did get a tiny "pfffft", hardly anything at all. He said that he had done this test after replacing the radiator and water just poured out which told him it was game over.
So I tested it using saran wrap and a rubber band to observe the fluctuations in pressure. And it occurred to me that it would be really cool to see how a "normal" S/V40 acts on this test.
Assuming you're smart enough to have always checked your fluid levels so you have never overheated your motor, do this:
On a cold motor, remove the coolant filler cap. Take about a 4" square piece of saran wrap and fit it down around the threads of the opening. Use a rubber band doubled over once or twice to make it tight, and then fit the band over the wrap and down around the bottom thread, securing the wrap. It shouldn't be skin-tight but not too loosey goosey either, just "snug".
Ask a helper to start the vehicle and idle it as you observe the action of the saran wrap.
On ours, (which was not stone cold but almost), startup seemed to suck the wrap down slightly, then it recovered, and then it slightly puffed out a bit, then down, then out as fluid began circulating as well as heating.
After maybe a minute or so, it did begin showing obvious pressure buildup but it wasn't really strong. Then we revved to around 2000 or so and the pressure, while changing up and down, seemed to remain fairly constant, and then after maybe another minute, a pinhole appeared in the now-golf-ball-sized balloon so we shut it off at that point.
If you're in the mood, it would really be cool to see a short video clip of this being done. I realize this is asking a lot but I'm sure there are others just as geeky as I am that would do this.
Hello my names Noah, I was curious if you guys could help answer a few engine swap questions I have about my 2002 Volvo s40. I'm looking to actually swap out the engine due to the fact that it has 150,000 miles on it and I'm looking for more power. The engine in it right now is a inline 4 1.9L turbo, I'm also curious with the additional power brought by a bigger engine what other parts I would need to upgrade to be able to handle to additional power. I'd be interested to hear peoples opinions on the most powerful wreplacement engine that'll still allow me to be used it as a everyday driver.
You should take it to the dealer instead. It will cost you a diagnostic fee, but the dealer can hook it up to a computer diagnostic program called VIDA and look up Volvo-specific codes and be able to accurately tell what the problem is. All AutoZone will be able to do is pull the generic code, which will not give as much information as the code VIDA will give. You could take it to AutoZone, but if the code is caused by anything more than a loose gas cap, you may need X-431 Diagun diagnosed by the dealer anyway, taking it straight there will just save you some time. Hope this helps.