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Just wanted to clarify - the ECM relay gets power directly from the battery, it does not go through a switched source like the ignition switch. Because Nissan didn't think it thru and probably someone made a mistake and they just left it like that instead of issuing changes to the assembly line and all the crap that goes a long with that. Wait, don't you hear an audible "click" at that relay when turning the key from first position to second position? I haven't looked at the diagrams in a long time, but I believe the ECU gets constant power for some low-draw memory settings (which you can clear by unhooking the battery for 10 minutes).
When the ECU needs to run the car, it needs way more power, and to different pins, and that's when the ECM relay comes into play. I haven't looked at the diagrams in a long time, but I believe the ECU gets constant power for some low-draw memory settings (which you can cleared by unhooking the battery for 10 minutes). This would make more sense, but it seems strange to me that a PCB with a minimal amount of components would need anything more than a couple amps to run. The ECM relay DOES get power straight (fused) from the battery without going through any switched power source.
This is only theory in my head at this point and I wish someone else would chime in to confirm or disprove.
A smooth ride is something you should expect from your automobile and when everything is working properly you receive it. Compared to what has already been mentioned there are two other clues that are not major but still quite serious. You can check for yourself to see if the ignition coil is having trouble but do be careful.
In the interest of safety unless you are a very experienced mechanic and know your way around the electrical system, you ought to leave the repair work to a reputable automotive repair center.
The electrical system of the car operates efficiently when all parts are doing what is expected.
Ignition coil sends the electrical current from the battery to the spark plugs hence the engine starts. I think if you are clear about the concept of Transformer (Step Down) and its cause of damage, then you can easily understand the reason behind ignition coil failure.
If a car has a check engine light on and has P0171 and P0174 codes stored, the most likely cause is a vacuum leak.
Mass Air Flow (MAF)Another cause of P0171 and P0174 codes can be from a damaged mass airflow sensor.
Fuel Pressure Incorrect fuel pressure from the fuel pump can also rarely cause a lean condition.
We recently had a check engine light come on and after having it scanned at a local parts store we replaced an oxygen sensor. Joey, the most common vacuum leak on Explorers (around your model year) is from the intake manifold seals. Hey I found failure in my explorer 2000 in fact it was a vacuum leak, I bought some carb-clean and spray it around the upper engine running and it leak, so I took the intake out and put some engine sealer took me like and hour now my car feels great, thank you very much Dennis, you are a great dude. Eddie, I would double check to make sure the correct sensor (there’s four total) was replaced.
Hey Dennis, my car (Explorer 2000) is showing a code and it says P1309 No DTC definition found.
Jerry, After clearing the codes, if the computer sees the same fault is present it will set the code.
If I notice that a hose is a little cracked but not all the way through should I still replace it? If all the codes are now gone except the P1000 there’s probably not a fault to worry about.
Hi Dennis,I found a rubber hose elbow that collapse dimple inward on the back of intake the connects via rubber and plastic hose to the driver side valve cover, took battery off for 15 mins, turn car on No CEL after 2 hours of driving. On vehicles built before 1996, 2 digit fault codes are set by the OBD I system instead of more comprehensive 4 digit P (power train) codes on vehicles built 1996 and later that have OBD II systems. I would check specifications for fuel pump pressure – I think it should be more like 45 PSI. Codes p1399 p0301 p0302 p0303 p0304 honda crv, Check engine light came on yesterday and i got these codes from it.
If white wire is constant power from the battery, why is there a need to have a relay to distribute the same power to the ECU?
The same wire that feeds the ECM relay also feeds directly to the ECU without a switched source or another relay. It leads back to my original question, why a relay - why not reduce complexity and wire power directly. The reason why it's not on all the time must be because the ECU must complete the ground for the ECM relay coil (white green) at some point, whether it be accessory power, on power, or start signal.
The ignition coil can be thought of as part of the relay system which takes electrical current from the battery and sends it on to the spark plugs. Spark plugs will rely on the ignition coil to get necessary charge and problems getting the car started can hint of trouble around the ignition coil.


You will be dealing with electricity and will need not only eye protection, but proper insulation as well. It seems somewhat strange that something as small as the ignition coil can cause the kind of problems it does.
No doubt it plays a very significant role for the engine so it is needed to be well maintained. Ignition coil should be replaced whenever required as it plays an important to run the engine. Same reason heat and vibration caused due to high voltage current which burns the coil’s internal insulation either at primary or secondary winding.
Ignition coil really does a lot for smooth ride of the vehicle and it’s not good to carry on with a faulty one.
These codes are set by the car’s computer when it sees too much oxygen in the exhaust. If the reading from the mass airflow is incorrect, the computer can be doing its calculations with wrong numbers. The fuel pump regulator could be allowing the wrong amount of pressure to be pumped to the fuel injectors. If a fuel filter is clogged or restricted this can alter the amount of fuel that reaches the injectors also.
The parts store employee had recommended the oxygen sensor replacement however the code quickly returned.
They are small rubber type seals that fit into recessed grooves on the underside of the upper intake.
I have changed out the sensor with a new one on drivers side closest to the bumper, wiped out the codes with scanner but the code still shows up. The check engine light came on several months ago and I had it checked and it read lean gas.
The ECU is already being fed power from the white, and that is the same power to the relay, so why the need for the relay?
The ECM relay is powered by the white wire and makes a connection from (again) the white wire to the orange blue wire, which then in turn feeds the rest of the ECU circuits. This would agree with what I'm seeing in the FSM for the 93 models, as well as agree with the simple logic D unit is talking about. Then your vehicle is no longer running smoothly, but sputtering with jerks and stalling and other problems. Fuel which has not been ignited goes through the exhaust system and can do some very serious damage in the exhaust system. Moreover, there is a chance in working with the ignition coil that you could accidentally cause damage to the spark plugs. Thanks for providing so much info on vehicle ignition coil, especially the symptoms of a bad ignition coil. Of course everyone wants error free drive but it’s not what always happen, we need to make a little effort for it. Fuel pressure is not likely to cause lean conditions though, due to the computer’s ability quickly compensate and adjust the air fuel mixture. We thought maybe we had a defective part, so they exchanged them and we installed the parts again to no avail, it was still stalling. A smoke test if properly done will help find the leak, no matter if it’s a PCV elbow or anything else. Two days of driving the car the engine system fault tranmission fault light came on and the begin to idle while in park or stopped at the light.
The fault can many times be a bad O2 (Oxygen Sensor) sensor, also called an Air Fuel Sensor on Toyota. It idles rough, and when starting to drive from a stop position sometimes it spits and sputters. Is it for an audible diagnostic function, as in you hear the relay click so you know there is power being distributed to the rest of the circuits inside of the ECU? This is how I understand it, which would mean the ECM relay is on all of the time, as long as it's connected to the battery? Thick, black smoke will come from the tailpipe and if you can smell the scent of gasoline, you have an issue that needs your attention. This device to be connected to the primary terminals of the coil to read what the ohms are (a well-functioning ignition coil is going to register from 0.4 to 2 ohms).
If the computer sees more air entering the engine than what is actually going in it will enrich the mixture. After buying a fuel filter and going home my husband was about to install it when I searched online and found your article.
Meaning it may be best to check for a vacuum leak when the engine is cold and heat expansion has not sealed the gaps temporarily.
There are several people on Jeep forums that have replaced the MAP sensor and ECM (Electronic Control Unit) for this particular problem. I took it to the shop for a smog after driving the car for two weeks and two of the computers hadn’t reset. It has to do with the computer running a self check which can take several drive cycles meeting specific criteria.


I suggest letting a shop keep the vehicle over-night so it can be properly smoke checked in the morning when it is cool.
While it is true this is not a problem with the distributor or major parts electrical system, the ignition coil is still not generating what is needed. But fuel economy may also be the result of other problems not related to the ignition coil at all. Ignition coil difficulties could have a negative impact on your exhaust system which you do not want to have. The tips added here to detect whether the ignition coil is shorted or not seems a bit risky. Therefore if the computer sees less air than what is actually going into the engine it will decrease the amount of fuel in the mixture. After explaining to my husband that the cause could be from a leaky vacuum hose, he ran the car with the hood up and we could hear hissing.
We took the car to the Ford garage and had that changed, but it was still not running right.
You may want to leave the vehicle at the shop overnight so the technician can check it cold. The vehicle has to be driven certain lengths of time and under certain conditions before the computer will finally remove the P1000. I understand the symptoms and the importance why it is needed to be replaced but what is the reason behind its damage? Just because the code is related to oxygen sensor readings, it doesn’t mean that the oxygen sensors are bad. Mass airflow sensors can be damaged by dirt getting past the air filter and sometimes from oil that can come off of aftermarket air filters such as K&N. BTW – the reason the code was not triggered for awhile after it was cleared is because the computer requires some time, called drive cycles in order to monitor data and determine if there is a fault present after codes have been cleared. You do not want to have your car suddenly stopping or the fuel economy impacted by the part that needs to be replaced.
If both of these codes are stored this means that both banks of the engine have excessive oxygen in the exhaust.
K&N air filters have to be lightly oiled and if excessive oil is applied some of it can come off and end up in the mass airflow sensor. If the data monitored is not within a certain predetermined range, called parameters the code will be set and the CEL (Check Engine Light) will come on.
If you see the warning signs do not hesitate to have professional attention be given to the ignition coil.
If the oxygen sensors are replaced it’s most likely that the same codes will reappear. Although the parts store employee was trying to be helpful he was recommending replacing parts that were not bad. Since there’s not much clearance, it can interfere with cam sensor and ruin it in the process.
Another way to check for a vacuum leak is by using a propane bottle with the hose attachment.
I don’t think he was doing this intentionally, but it was starting to cost us an arm and a leg! No telling how long this would have gone on, but with your help we were able to repair the problem ourselves and not continue throwing money at the problem.
By introducing propane to the area where the suspected leak is you can sometimes notice a change in the idle. It’s important to install the replacement cam synchronizer in the same clock position, or a code may be triggered again. If this doesn’t fix the issue it may be time to let the Jeep dealership diagnose it rather than throwing expensive parts at it. If you have access to a scan tool, checking the oxygen sensor readings or fuel trim can be done while checking for leaks with propane. If the readings increase when you are adding propane to be suspected leak area, this indicates a vacuum leak. Evaporative leaks have to do with fuel vapors and a smoke machine is used to find those leaks. To check for engine vacuum leaks with a smoke machine, just find a vacuum hose that goes to the engine and attach the hose on the machine. When the smoke machine is turned on, smoke will enter the engine and help reveal the vacuum leak source.
It is common for some smoke to come out out certain areas without indicating a vacuum leak, so if you think you’ve found a leak with the smoke is best to double-check it to make sure.



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