For most tests you want the circuit loaded, meaning operating in their normal state. You could get a voltage reading of 5V (which most sensors use) if you unplug it and read circuit voltage. But current isn't actually flowing so until it is loaded, you don't really get an accurate reading. Think of a car battery that reads 12V on a meter, but yet won't start the car. Until current is actually flowing you don't know the actual voltage being supplied. Voltage is "potential". (Side note: Don't get me wrong, there are also readings you will take for various tests where you will have sensor unplugged.) So, the T-pins are used to probe the back side of your connector while it still plugged in to a sensor and in its normal state. The last thing you want to do is start shoving meter leads into connectors. You never want to do that! Either on the front side or the backside of a connector. You deform the contacts and create a whole new problem.

 

Sure there is possibility for bad O2 sensors, but they are at the end if the chain. They may be operating perfectly but are trying to compensate for bad data being put to the VCM by input sensors, timing problems, spark problems, fuel problems, etc, etc at the begining of the chain.

 

Ok, thanks for clarifying the T pins and the O2 sensor for me.

 

Example of using a T-pin:

 

Just a note about the pic above to be safe since it might be hard to see. I only have one T-pim inserted (the black test lead was connected to B-). As a practice you don't want to install two T-pins and have them touch and short out a sensor (or worse).

 

Ok, now I understand the reasoning for their use. Thanks for the pics.

 

OK Ken I'll stay with you. The reason why we do the cold key on engine off readings is to see if the relevant sensors look OK:

1. IAT look perfect because you read 48.2F with an ambient of 48F
2. MAP also looks good 29.83 vs 29.94
3. ECT or its wiring may have some problems because it read 42.8F vs 48F. Your warm engine temp also looks high especially given a 48F ambient
4. We better check your TPS. Key on engine off, watch TPS in live data as you smoothly move the accelerator pedal from idle to the floor and back. You should get a smooth reading up and down from roughly zero to 100% and back.
5. We need all three O2 sensors, usually labeled B1S1, B2S1, and B1S2 or B1S3. The one you graphed has problems, what we don't know yet is if its the senor, the wiring or an accurate report with an out of bounds fuel delivery problem. I will comment more after we get all three graphs
6. We need your warm running data at idle and 2500 rpm, ill explain why after we get the data
7. We will need your MAF reading at the point of a full throttle 1-2 shift, i will explain later.

Regarding your fuel trims, a large positive number (always add ST and LT together for a given bank) means that the computer started with a theoretical fuel delivery amount based on the sensors that are not O2 sensors like MAF, MAP, TPS, ECT, ... but when the engine is in closed loop the O2 sensors always run the show and constantly modify fuel delivery to stay at 14:1 air/fuel delivery. If there is a big difference between these two values then you get very high fuel trims and something is wrong, we dont know what that is yet but were going to find out. Either:

1. You have unmetered air like a vacuum leak, the 2500 rpm data will help us with this
2. You have a fuel pressure or injector problem and low fuel delivery
3. The O2 sensors, their wiring or the engine computer is faulty
4. You have an exhaust leak
5. There is an engine mechanical problem
6. There is a sensor problem

I'll stick with you as long as you want my input, your in charge of that part.

George

 

Thanks George for the advice and sticking with me on this. I'll get the data and post it tomorrow or the next day. Again, thanks!

 

My pleasure

George

 

Since you guys are talking about test lights and you seem to want to learn:

A test light is an invaluable testing device for diagnosing vehicles. Besides showing if a signal or voltage is present it can also load the circuit under test. This can be good or bad. If your testing say the O2 sensor heater circuit then the current draw of an old school incandescent test lamp is perfect because it tells you that the circuit can probably supply the current that the heater needs and maintain proper voltage levels. An LED test lamp draws almost no current so it will tell you that voltage is there but it wont load the circuit so the problems of say a corroded power or ground wire may not reveal itself. This same excellent old school test light can cause damage however if not careful. Some of the sensor power switching back at the engine computer can be unprotected and sensitive to excessive drive currents either as a positive voltage source or ground side switching. Unless you are sure of what you are doing an LED test light is way safer around computer circuits.

George