hey all, my car has been picky lately and has been randomly giving me a P0101 code (MAF sensor error). In doing some troubleshooting, I have found that at idle the car pulls around 5 grams/sec of air which is a good reading. Disconnecting one MAF sensor at a time, the air flow drops by half (to 2.5 grams/sec). So, that part seems to be working as it should. This is where I am confusing myself and am looking for clarification. When I unplug the MAF sensor on the Bank 1 side (passenger side for a US vehicle), the IAT temp drops from 90F to -40F. If I plug in bank 1 and disconnect bank 2, the IAT temp stays constant at 90F. I am looking to make a little jumper plug to slide between the MAF sensor and the factory plug to allow me to take some readings to verify the IAT voltages. Granted, doing some learning about MAF sensors, I am trying to figure out if we have digital or analog MAF sensors. This makes how you check the voltage change. The analog you use a multimeter. The digital one, you need an o'scope (I have one, so, I am good there).

Any info would be greatly appreciated.

 

I don't know but I'll bet one of the tuners would know like Velocity or ETG

 

XJsss, well, I have been watching some Youtube videos and doing some other research and from what I can tell, it is my Bank 2 side that is having issues. I need to pull out my tools and do some voltage measurements. I just happen to have a spare MAF sensor and put it in already and that didn't change things. So, unfortunately, I am most likely looking at a bad wire somewhere between the MAF sensor and the ECU. So, this should be fun. The only other issue that it could be would be if the ECU took a dump on that one sensor. But, my voltage measurements should tell me that.

 

Probably the power for the IAT comes through that MAF sensor. GM does that with the TPI system a lot. Haven't dug into the Jaguar so it would be a learning experience for me. Do you have a vacuum leak after the MAF's? At idle it may not appear as big, but at higher RPM's would appear greater. If you get down to wiring, check the pin grip on the connectors. Take a new pin and slide it on both sides and see if one is easier to pull off. A lot of times the connector on the engine will become intermittent due to the vibrations wearing out the pins. It may be fine at idle but will lose contact at higher RPM's with the higher vibrations. If you can't find anything wrong then follow the harness and disconnect and reconnect every connector up to the computer in case one has corrosion that's building. My experience is that they will most likely corrode at the firewall connector. Then shake down the harness on the engine to see if you can short it out. If that don't work then follow the harness on the engine and insulate it temporarily with plastic at each point the harness could short. If that fixes it then remove the extra insulation one at a time until it comes back. Lastly it could be an I/O circuit in the computer. Some modern electronics use really cheap capacitors that start to go out after five years or so. I would hope Jaguar would buy good quality Panasonic or Nichicon. Of course everybody troubleshoots their own way but that's how I would handle it. I wouldn't tear the harness apart until I proved it was bad. Too hard to put it back down. Same under the dash. If you were in a hurry you could just string a new wire temporarily and terminate both ends and bypass the harness completely. I've done that when I couldn't get to the harness just to figure out where the wire was grounding out but then that was in the pylon of a jet engine. It took three days to pull the engine and pylon and replace that one wire properly. You probably wouldn't be able to do that today, they are a lot more strict, they would probably want you to replace it properly the first time. When you have an intermittent problem though it's hard to say where it is. Process of elimination. Hop this helps a little.

 

rhomanski, the circuit is pretty simple. You have the ECU, 5 wires coming from it that go straight to the MAF/IAT sensor (2 sensors in 1) on each side. From my testing, the MAF sensor on both sides seem to be working just fine as I get a good MAF reading at idle and when I undo the one, the reading falls by half (what I would expect). But, undoing the IAT sensor on each side, one side reads the same, the other falls to -40F (which seems to be the low end of the allowable reading.

I was hoping someone would know whether we have digital or analog sensors as the testing for these is slightly different. I am hoping that I can get a difference in the readings for the bad IAT between the connection at the ECU and at the MAF/IAT itself. That would confirm that it is a wiring issue. Otherwise, it pretty much only leaves the ECU.

I have been battling the P0101 code and it seemed to pop up its head right after I did the K&N filter change over. So, I blamed it on that. But, I have since gone back to normal filters and the code is still locked in. So, it is looking like I have an actual problem. Now to figure out how the connectors come apart. I am hoping that you are correct and it is nothing more than a connector that has loosened up/corroded and the fix is that simple. It would appear to be something that simple. But, I never have that good of luck when it comes to my own vehicles.

 

I see the MAF and IAT are in one sensor body. Where are you getting the readings from? A scanner on the computer?
I'm concerned by the difference in the IAT's then. They should both go to -40 when unplugged which would denote an open I would expect.
My old cars are strictly analog. New ones, I don't know.
I have heard of MAF's being damaged by too much oil on K&N filters. But the fact that you disconnect one IAT and it doesn't change at the computer is worrisome. That would seem like a high resistance short somewhere in the harness on the signal wire. I was ready to ignore it until you said the sensors are in the same body. In that case the computer may not set a separate IAT code but just set a MAF as your getting.
Do the temps read the same at the computer? Does the suspicious one change when it's idling outside versus in the garage? If the computer sees too great of a difference between the two it should set a code. Usually about 10 to 15 degrees.

 

rhomanski, I am using my Torque app on my phone via an ELM 327 unit that plugs into the OBD port. I do have a locked in error code which is P0101 which is for a failed MAF sensor. Unforunately, my code reader is not the enhanced version that would give me the dashed number after the P0101 number to be more specific as to what the problem is.

From my understanding of the ECU and its programming where it tries to compensate for known errors, I can see where unplugging the bad sensor would cause the indication to remain constant since the computer is ignoring that sensor. I know that if your crankshaft position sensor fails, it will ignore that and then look to the camshaft sensors to figure out where TDC is and then guestimate when the other cylinders should be fired. In the case of the MAF sensors, unplugging the bad MAF sensor should cause the IAT temp to remain constant and when the good sensor is unplugged, since the computer does not have something to contradict a reading, it has to use the bad signal. I will note that when I plugged what I think is the good MAF sensor, the motor definitely changed how it was running (based on the IAT temp changing dramatically, therefore making the computer think that more dense air is making it to the motor, therefore, adds more fuel to compensate). Where unplugging the suspected bad sensor had no effect on the motor that I could notice.

Of note, with both sensors plugged in, my reader said the IAT was seeing 91F (ambient temperature was like 60F, but I had just recently ran the car, so the motor was still warm). Unplugging the suspected bad sensor, the reader stayed at 91F. Unplugging only the suspected good sensor, the indication fell to -40F (which I believe is the low end "failed" point of the sensor which is what the computer uses to say that the sensor is failed). If it was reading say -39F, then the computer sees the sensor as reading something and therefore does not call it bad. All sensors have a high and low fail point built into them to allow the computer to determine which sensors are good and which are bad.

One of the checks that I am going to try is to connect the suspected bad MAF sensor to a multimeter set to resistance and then using a hair dryer, pass warmer air by the sensor. This should cause a change in resistance if it is functioning. Besides, I have swapped the suspected bad MAF sensor with a known good one with no change in indications.

As for excessive oil, I have been using K&N filters for 10+ years with no issues. So, I don't think the MAF error I have is related to the filters. Besides, if I had over oiled the filters, I should see oil inside the intake which I do not see.

I have not measured things at the ECU. I am attempting to find something better than simply sticking straight pins in along the wire and measuring things that way. Not sure which way I am going to jump at the moment, but I also want to get this resolved before things really go south on me.

 

It sounds like an analog signal to me. My old Corvette would read about -41 degrees when I would disconnect the outside air temp sensor. That sure got the heater going in auto. That's how I discovered the problem. it went to full heat one summer afternoon. With an aluminum intake like mine have, 91 is normal for a hot engine. The aluminum will warm the air as it goes through, now I understand the intakes are some sort of plastic? It probably shouldn't read 30 degrees higher in that case.

In your situation I would unplug the computer and check the resistance of the wire to the sensor that's not changing and if it's reading less then an ohm or thereabouts call the wire good. That would leave the computer. Before ordering one though, I would connect the computer back up and see if that fixed it. If the wire reads more than an ohm, I would look for connectors between the sensor and the computer and disconnect them and check them in both directions.

In the case of my Corvette the wire read open between the heater control and the OAT sensor. I disconnected the firewall plug, they called it the C100 plug. It was a dead short in both directions, so I cleaned the pins and covered it with fresh dielectric grease from GM. That plug hasn't had a problem in the twenty something years since.

My cousin bought a 2000 something Cadillac that would just stop running after about twenty minutes. He took it back to GM several times but they refused to see the problem. He got fed up and before he traded it in he opened up the ECU. He found a wire wound resistor that had cracked, probably from the robot arm stressing it when inserting it on the board, He replaced it with an old carbon resistor he had sitting around and never had that problem with the car again. He passed recently but he was very smart. He was an engineer developing the Mercury capsule and the Gemini capsule years ago, so he was a real rocket scientist. I sure do miss him. He had a solid brass model of a Mercury capsule with a plaque thanking him for his work the company gave him. I'd love to have it as a memento but I'm sure it's worth many thousands of dollars so his children should keep it. Collectors pay top dollar for things like that. I saw a plastic Apollo model given to another engineer that his family sold for $10 in a garage sale. The guy that bought it took it to New York and got $10,000 at auction.