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This is information I found on a Mopar chat site. Discussion centers around intake air temperature sensor resistance readings over operational temperature range. Vehicle in question is a 2001 Ram truck. I would think these values would be consistent across all Chrysler vehicle engines in the same time frame era ???

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Discussion Starter · #3 ·
This is information I found on a Mopar chat site. Discussion centers around intake air temperature sensor resistance readings over operational temperature range. Vehicle in question is a 2001 Ram truck. I would think these values would be consistent across all Chrysler vehicle engines in the same time frame era ???

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Thanks for the good info. I'll make some measurements to confirm.
 

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1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
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Are you having driveability or fault code issues with the IAT? I see 3 possible fault codes of P0111 (sensor performance), P0112 (voltage low/short) and P0113 (voltage high/open). See p. 54-58 here:
http://oskin.ru/pub/chrysler-dodge/manuals/Service Manuals/2002_RG_Town&Country_Caravan_Voyager/02rgep.pdf

Connector pinouts, wire colors and a simple wiring diagram are in the back of the book. Problems are usually the sensor itself, the related wiring or (lastly/rare) the PCM itself.
The sensor is a thermistor and is generally trouble-free and stays in calibration. I have had to replace them mostly from handling and physical damage.

I see a Mopar part # of 4606487AB. Go with an OEM part for best results.
An example: 4606487AB - Mopar Parts Giant (at https://www.moparpartsgiant.com/parts/mopar-sensor-charge-air-temp~4606487ab.html?Make=Dodge&Model=Caravan&Year=2002&Submodel=&Filter=() )
 

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Discussion Starter · #6 ·
Are you having driveability or fault code issues with the IAT? I see 3 possible fault codes of P0111 (sensor performance), P0112 (voltage low/short) and P0113 (voltage high/open). See p. 54-58 here:
http://oskin.ru/pub/chrysler-dodge/manuals/Service Manuals/2002_RG_Town&Country_Caravan_Voyager/02rgep.pdf

Connector pinouts, wire colors and a simple wiring diagram are in the back of the book. Problems are usually the sensor itself, the related wiring or (lastly/rare) the PCM itself.
The sensor is a thermistor and is generally trouble-free and stays in calibration. I have had to replace them mostly from handling and physical damage.

I see a Mopar part # of 4606487AB. Go with an OEM part for best results.
An example: 4606487AB - Mopar Parts Giant (at https://www.moparpartsgiant.com/parts/mopar-sensor-charge-air-temp~4606487ab.html?Make=Dodge&Model=Caravan&Year=2002&Submodel=&Filter=() )
There are no IAT codes, and I now find that the IAT sensor is fine, but thought this might have been related. Am seeing occasional P0171 (Lean fuel trim), occasional stumbling/rough idle when cold, and pinging under heavy load. No other related sensors appear to be faulty, and I don't detect any significant vacuum leak. The long term fuel trim (+15% to low +20% range) appears some at idle and maxes out at a couple of thousand RPM under no load, and goes to near zero while driving. I'll be looking at the EGR next. The PCV valve seems to be working, but I haven't removed it to perform the rattle test yet. One curiosity is that the throttle position sits at about 16% when closed, but from what I've read, this may be in the normal range, and the throttle position readings are smooth over the entire range.
 

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. . . .Am seeing occasional P0171 (Lean fuel trim), occasional stumbling/rough idle when cold, and pinging under heavy load. No other related sensors appear to be faulty, and I don't detect any significant vacuum leak. The long term fuel trim (+15% to low +20% range) appears some at idle and maxes out at a couple of thousand RPM under no load, and goes to near zero while driving. . . . .
One would expect that a high, positive fuel trim at idle indicates a vacuum leak (extra air) into the induction system. The PCM (powertrain control module) compensates and attempts to add extra fuel to keep the air- fuel mixture ideal / stoichiometric. If the fuel trim approaches zero at higher engine rpms then the extra fuel added / calculated by the PCM due to throttle position, etc. starts to mask the need for extra fuel through the fuel trim logic and thus reduces fuel trim values to near zero. So I am thinking you have a very small vacuum leak. Check every vacuum hose at each end for cracking, brittleness, hardness. Check hose to power brake booster at both ends. You can remove the vacuum hose to the brake booster, plug it and run a test to see if the brake booster assembly is leaking. Engine heat causes hose ends to harden and lose elasticity and that can cause a leak.

With the engine in closed loop mode and idling spray a small quantity of carburetor cleaner into the intake system. The oxygen sensor should go rich and the fuel trim go negative as the PCM adjusts and tries to keep the air - fuel mixture at stoichiometric or balanced conditions. This test lets you know that the oxygen sensor are functioning properly and the PCM is receiving correct signals from its sensors.
 

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Look at the 'Possible Causes' for P0171 in the diagnostic book.
It could be a defective O2 sensor. I have also had problems with brand new aftermarket (non-OEM) O2 sensors, namely Bosch. Is fuel pressure OK?
A vacuum leak would tend to raise idle speed, so much so that the IAC may not be able to back down the RPM and set a P1299 code. Listen for a change in engine idle sound while pinching the p/brake booster vacuum hose with pliers.
Fuel trim generally shouldn't vary more than + or - 10% on a healthy system.
A 16% throttle opening should be fine with no other symptoms. It is possible that a previous owner or technician may have tampered with the 'minimum air' screw to compensate for low or rough idle.
 

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Discussion Starter · #9 ·
One would expect that a high, positive fuel trim at idle indicates a vacuum leak (extra air) into the induction system. The PCM (powertrain control module) compensates and attempts to add extra fuel to keep the air- fuel mixture ideal / stoichiometric. If the fuel trim approaches zero at higher engine rpms then the extra fuel added / calculated by the PCM due to throttle position, etc. starts to mask the need for extra fuel through the fuel trim logic and thus reduces fuel trim values to near zero. So I am thinking you have a very small vacuum leak. Check every vacuum hose at each end for cracking, brittleness, hardness. Check hose to power brake booster at both ends. You can remove the vacuum hose to the brake booster, plug it and run a test to see if the brake booster assembly is leaking. Engine heat causes hose ends to harden and lose elasticity and that can cause a leak.

With the engine in closed loop mode and idling spray a small quantity of carburetor cleaner into the intake system. The oxygen sensor should go rich and the fuel trim go negative as the PCM adjusts and tries to keep the air - fuel mixture at stoichiometric or balanced conditions. This test lets you know that the oxygen sensor are functioning properly and the PCM is receiving correct signals from its sensors.

I'll recheck for vacuum leaks. I did note, however, that when checking the PCV valve, when removed the vacuum hose and allowed a very large vacuum leak, then engine RPM increased greatly, but the fuel trims did not. Maybe there is a clue in that.

The O2 sensor is new and seems to work fine in closed loop under any reasonable load. The old one had some problems, but driveability was not really any different.
 

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Discussion Starter · #10 ·
Look at the 'Possible Causes' for P0171 in the diagnostic book.
It could be a defective O2 sensor. I have also had problems with brand new aftermarket (non-OEM) O2 sensors, namely Bosch. Is fuel pressure OK?
A vacuum leak would tend to raise idle speed, so much so that the IAC may not be able to back down the RPM and set a P1299 code. Listen for a change in engine idle sound while pinching the p/brake booster vacuum hose with pliers.
Fuel trim generally shouldn't vary more than + or - 10% on a healthy system.
A 16% throttle opening should be fine with no other symptoms. It is possible that a previous owner or technician may have tampered with the 'minimum air' screw to compensate for low or rough idle.
Good thought. The new O2 sensor is a possibility - no name brand, and I had wondered if it was possible that the new sensor is as bad as the old one. The old sensor occasionally threw an O2 heater code, but otherwise the symptoms were the same.The fuel trims look good under power, though, so wonder if the O2 sensor could actually be involved. It gets warmer under power - maybe that's enough to make the difference.

I'll try the brake booster hose as you and AlanC suggest.
 

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. . . I did note, however, that when checking the PCV valve, when removed the vacuum hose and allowed a very large vacuum leak, then engine RPM increased greatly, but the fuel trims did not. Maybe there is a clue in that. . . . .
Creating a vacuum leak through the brake booster hose is similar to opening of the throttle plate. More air is allowed into the engine, the intake manifold vacuum decreases indicating more air mass moving through the engine. The PCM adjusts the pulse width of the injector to add more fuel to keep the air - fuel mixture very close to stoichiometric / chemically balanced. When you add more fuel and air to the engine it runs faster. So this is expected behavior.

. . . . The O2 sensor is new and seems to work fine in closed loop under any reasonable load. The old one had some problems, but driveability was not really any different. . . .
Did you run the test where you inject small quantities / bursts of carburetor cleaner into the intake air stream? With this test you are creating a temporarily rich air - fuel mixture. The oxygen sensor should detect this and indicate a rich condition with voltage greater than 0.45 volts. The PCM sees this rich mixture as reported by the oxygen sensor and then temporarily decrements the fuel trim value to a negative % value. You should see fluctuations in the oxygen sensor reading and fuel trim values if these components are functioning properly.
 

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Pulling the PCV valve and/or introducing a vacuum leak on an idling engine will make RPM increase. This is normal. The MAP will compensate for the added air by adding fuel. This will keep the air/fuel ratio happy.
The O2 sensor at warm idle should always be changing high/low rapidly (approx 0.2v-0.8v). If it sits still in the middle (approx 0.45v) or 'pegs' high or low, then there is a problem.
A shot of solvent into the throttle body should cause a O2 voltage and short-term fuel trim reaction as the O2 senses the increased richness by 'sniffing' the oxygen content of the exhaust gases.
Unknown or 'universal' O2 sensors may be a problem. I have always gone with OEM (Mopar or NTK/NGK) after getting burned in a diagnosis that pointed to a bad O2 sensor.
The problem remained after replacing the O2 with a new part. I began looking elsewhere for the problem and wasted a lot of time while the problem was with the new (non-OEM) O2 sensor:
warning on bosch o2 sensors - DodgeForum.com (at https://dodgeforum.com/forum/3rd-gen-ram-tech/315149-warning-on-bosch-o2-sensors.html )
 
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Discussion Starter · #14 ·
Pulling the PCV valve and/or introducing a vacuum leak on an idling engine will make RPM increase. This is normal. The MAP will compensate for the added air by adding fuel. This will keep the air/fuel ratio happy.
The O2 sensor at warm idle should always be changing high/low rapidly (approx 0.2v-0.8v). If it sits still in the middle (approx 0.45v) or 'pegs' high or low, then there is a problem.
A shot of solvent into the throttle body should cause a O2 voltage and short-term fuel trim reaction as the O2 senses the increased richness by 'sniffing' the oxygen content of the exhaust gases.
Unknown or 'universal' O2 sensors may be a problem. I have always gone with OEM (Mopar or NTK/NGK) after getting burned in a diagnosis that pointed to a bad O2 sensor.
The problem remained after replacing the O2 with a new part. I began looking elsewhere for the problem and wasted a lot of time while the problem was with the new (non-OEM) O2 sensor:
warning on bosch o2 sensors - DodgeForum.com (at https://dodgeforum.com/forum/3rd-gen-ram-tech/315149-warning-on-bosch-o2-sensors.html )
I've now checked all the vacuum ports (removed hosed and plugged the hole for each one) without any effect on the idling fuel trim. PCV is ok, and EGR acts ok, but haven't removed the EGR to inspect and clean. Now, after new plugs and manually moving the EGR diaphragm along with some added throttle ( that EGR tweak has removed stumble at low speeds in the past), the driveability issues are gone and the spark knock under heavy load is almost gone. The high idle fuel trim remains, now around +14, and I've noticed a few times that the fuel trim will go to 24.2 (just shy of the magic number 25, which throws the lean fuel trim code) on long, engine braking, no- throttle but moderately high RPM descents in lower gear. It seems like a small vacuum leak would have less effect in a high rpm, high vacuum situation, but the PCM says is gets leaner. Fuel trims under load remain near zero.

I've not yet tried the solvent method, but since the short term trim is constantly moving, I presume the O2 sensor is at least not stuck at a constant voltage. I'm using a Blue Driver OBD II tool, and I've yet to figure out how to display raw O2 sensor voltage.
 

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. . . .The high idle fuel trim remains, now around +14, and I've noticed a few times that the fuel trim will go to 24.2 (just shy of the magic number 25, which throws the lean fuel trim code) on long, engine braking, no- throttle but moderately high RPM descents in lower gear. It seems like a small vacuum leak would have less effect in a high rpm, high vacuum situation, but the PCM says is gets leaner. Fuel trims under load remain near zero. . . .
It is possible to have an exhaust system leak at the gasket surface between exhaust manifold and head or a leak at the exhaust flange fitting adjacent to the upstream oxygen sensor. Is the oxygen sensor tight in its mounting on the exhaust pipe? Extra air introduced at these locations will cause the oxygen sensor to report a leaner combustion event than actual. This then causes the PCM to enrich the air - fuel mixture more than necessary.
 

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Discussion Starter · #16 ·
Pulling the PCV valve and/or introducing a vacuum leak on an idling engine will make RPM increase. This is normal. The MAP will compensate for the added air by adding fuel. This will keep the air/fuel ratio happy.
The O2 sensor at warm idle should always be changing high/low rapidly (approx 0.2v-0.8v). If it sits still in the middle (approx 0.45v) or 'pegs' high or low, then there is a problem.
A shot of solvent into the throttle body should cause a O2 voltage and short-term fuel trim reaction as the O2 senses the increased richness by 'sniffing' the oxygen content of the exhaust gases.
Unknown or 'universal' O2 sensors may be a problem. I have always gone with OEM (Mopar or NTK/NGK) after getting burned in a diagnosis that pointed to a bad O2 sensor.
The problem remained after replacing the O2 with a new part. I began looking elsewhere for the problem and wasted a lot of time while the problem was with the new (non-OEM) O2 sensor:
warning on bosch o2 sensors - DodgeForum.com (at https://dodgeforum.com/forum/3rd-gen-ram-tech/315149-warning-on-bosch-o2-sensors.html )
The upstream O2 sensor rapidly changes between about 0.1 and 0.8 volts. Downstream is pretty steady at about 0.745 volts.
 

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Discussion Starter · #17 ·
It is possible to have an exhaust system leak at the gasket surface between exhaust manifold and head or a leak at the exhaust flange fitting adjacent to the upstream oxygen sensor. Is the oxygen sensor tight in its mounting on the exhaust pipe? Extra air introduced at these locations will cause the oxygen sensor to report a leaner combustion event than actual. This then causes the PCM to enrich the air - fuel mixture more than necessary.
The O2 sensor is tight - will check for exhaust leaks elsewhere. Based on the very small response to intentionally introduced vacuum leaks, if a leak is the problem, the exhaust side seems more likely. There is a small oil leak at the head gasket on #4 cylinder, but no exhaust leakage that can be felt there, so I doubt it's pulling in air.
 

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. . . . The upstream O2 sensor rapidly changes between about 0.1 and 0.8 volts. Downstream is pretty steady at about 0.745 volts. . . .
The equilibrium point at which the oxygen sensor reports neither a rich nor lean condition is 0.45 volts. The upstream oxygen sensor is oscillating between 0.1 volt / lean condition and 0.8 volt / rich condition. If that is indeed correct data then the fuel trim should also oscillate between a lean condition (negative value less than 0..0 %) and rich condition (positive value greater than 0.0 %). Yet the fuel trim is +14% and sometimes greater.

Which fuel trim value are you observing? There is a short term fuel trim value and a long term fuel trim value. I could see a situation where the short term fuel trim is oscillating between a small negative % and a small positive % which is optimum and the long term fuel trim would be at +14 %. But in that scenario the long term trim at +14% is out of normal range.

I wonder if the PCM is in closed loop mode? Closed loop occurs when the oxygen sensor reaches at least 600 deg F or higher temperature and the PCM starts using the values from the oxygen sensor to help in calculating air - fuel mixture. If something were keeping the PCM from going into closed loop mode and remains in open loop, the PCM ignores oxygen sensor readings for calculating air- fuel mixture. Is there a data pid on your monitoring device to indicate OPEN or CLOSED loop mode?
 

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Discussion Starter · #19 ·
The equilibrium point at which the oxygen sensor reports neither a rich nor lean condition is 0.45 volts. The upstream oxygen sensor is oscillating between 0.1 volt / lean condition and 0.8 volt / rich condition. If that is indeed correct data then the fuel trim should also oscillate between a lean condition (negative value less than 0..0 %) and rich condition (positive value greater than 0.0 %). Yet the fuel trim is +14% and sometimes greater.

Which fuel trim value are you observing? There is a short term fuel trim value and a long term fuel trim value. I could see a situation where the short term fuel trim is oscillating between a small negative % and a small positive % which is optimum and the long term fuel trim would be at +14 %. But in that scenario the long term trim at +14% is out of normal range.

I wonder if the PCM is in closed loop mode? Closed loop occurs when the oxygen sensor reaches at least 600 deg F or higher temperature and the PCM starts using the values from the oxygen sensor to help in calculating air - fuel mixture. If something were keeping the PCM from going into closed loop mode and remains in open loop, the PCM ignores oxygen sensor readings for calculating air- fuel mixture. Is there a data pid on your monitoring device to indicate OPEN or CLOSED loop mode?
Yes, there is a fuel system monitor for open/closed loop operation. Once operating closed loop, the long term trim is around 14% and fairly steady at idle, with the short term oscillating around zero by a couple of %. When changing from one adaptive memory cell to the next, the short term may increase to the large value while the long term slowly catches up. During that transition, the sum of the two is about where the long term trim settles.
 

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. . . . Once operating closed loop, the long term trim is around 14% and fairly steady at idle, with the short term oscillating around zero by a couple of %. . . . .
Now the results are making more logical sense. Short term fuel trim oscillating around 0%, oxygen sensor oscillating between rich and lean with long term fuel trim at a higher than normal range value. My comment previously about an exhaust system leak is not relevant and incorrect and was based on the false assumption that the short term fuel trim was stuck at a rich 14%.

For some reason the engine is getting less than the baseline fuel delivery that is programmed into the PCM. The PCM is increasing fuel delivery to get the air - fuel mixture close to expected baseline values. That is why the long term fuel trim is at +14%. I would check fuel system pressure to make sure it is within specification of 58 psi +- 5 psi. If fuel pressure is slightly below specification, this would cause lower than expected fuel delivery for baseline setting and cause the PCM to increase the long term fuel trim.
 
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