p0128 Engine temp below thermostat temperature/ strange O2 sensor values

[nonickatall]

Hello, I was just driving and suddenly the engine light came on. I read it at home and found that I had a P0128. This means the "engine temperature is below the thermostat temperature".

In other words, the engine complains that it isn't warming up properly. Since the beginning I've had the feeling that it's not warming up correctly. I had already changed the thermostat and things got a little better after that, but the car still doesn't get really warm. My temperature is always around a quarter. He rarely reaches the middle. My heating isn't getting really warm either.

Now, following a feeling, I looked at the O2 sensor values. And they seem quite strange to me. Please refer:

The O2 sensor in bank 2 is stable at around 700 mV, while the O2 sensor in bank 1 constantly fluctuates back and forth between 60 and 700 mV. That can not be normal?

Has anyone had this before? Do you think it's more likely to come from a defective O2 sensor, or is it more likely from an injector that's no longer working properly?

Ideas?

 

[strutaeng]

O2 sensors don't appear to be switching but it's better to see them in graph waveform if available. It may be related to the low temperature though. I would figure that out first.

 

[Scottydoggs]

see if you got other o2 items to scan. ho2 iirc is the heater inside the o2. it warms up the o2 sensor when cold to speed things along. even if it was to set a code for the heater being bad, just that wont affect how it runs.

once you got the right o2 pid's to scan, take it for a ride go wot, the Mv should be reading 930 ish and lock in there till you let off the gas, if it drops or dont get up into the high 800's the o2 is bad/lazy. when at idle/cruise its going to move up and down and never be steady. the wot part is what matters. you can also check Voltage on the o2's. at idle its should be bouncing up and down 1-9 pretty fast.

you can also check your long term and short term fuel trims off each o2. just sensor 1 on both banks. sensor 2's reading will not mean much as all they really do is tell you if the cats are bad. up stream is what works with your fueling.

as far as the running cold. try blocking off 1/2 the rad with some cardboard. when you replaced the t stat was it a 195 temp? a 160 could set that code as its opening to soon and it never gets to full temp during the colder months.

 

[Fless]

I'd concentrate on the cold temp issue. With a scanner check the PID for engine coolant temp to see what it shows.

Any chance the radiator has been replaced at some point? Some aftermarket radiators lack the necessary restriction in the fitting to the hose that goes to the surge tank. Too much flow in that hose can keep the engine temp low. If you suspect that's the case, temporarily pinch it to reduce (not stop) the flow and see how the engine temp reacts.

Your "Sensor 1" O2 values should be changing from 100 to 900 mV regularly, as long as the circuit is in closed loop; these pre-cat sensors tell the PCM how to control the metering of fuel to the cylinders. Sensor 2s are after the cats and are much more stable, and do nothing but indicate catalytic converter efficiency.

 

[adventurenali92]

I'd concentrate on the cold temp issue. With a scanner check the PID for engine coolant temp to see what it shows.

Any chance the radiator has been replaced at some point? Some aftermarket radiators lack the necessary restriction in the fitting to the hose that goes to the surge tank. Too much flow in that hose can keep the engine temp low.

Your "Sensor 1" O2 values should be changing from 100 to 900 mV regularly, as long as the circuit is in closed loop; these pre-cat sensors tell the PCM how to control the metering of fuel to the cylinders. Sensor 2s are after the cats and are much more stable.

I was gonna suggest the radiator thing as well for the cause of the low temps.

 

[rockola1971]

My bet is you didnt put in the correct temp rated thermostat. The opening temp rating is usually stamped on the thermostat. Pop it out and look. You have a scanner it will show at what temp value the thermostat opens up. Watch for the temp to raise from a cold start and then when it suddenly starts to drop back down a little, that will be roughly the opening temp rating.

 

[nonickatall]

My bet is you didnt put in the correct temp rated thermostat. The opening temp rating is usually stamped on the thermostat. Pop it out and look. You have a scanner it will show at what temp value the thermostat opens up. Watch for the temp to raise from a cold start and then when it suddenly starts to drop back down a little, that will be roughly the opening temp rating.

No, i especially looked for the right temperature thermostat when i ordered it at rockauto. But the idea is good.

The radiator hint from @Fless is a hit. If there is some kind of restriction, which is missing, it would explain that behave. I would never had that idea.

But will check tomorrow the resistance of the temperature sensor for the gauge and the ecm first.

I guess the truck hat two different like in most cars, or am i wrong?

I must google tomorrow first, where the sensors are, and what resistance readings are correct, to make sure that I not search for a problem, based of wrong measured values.

If that is correct, i will check for the radiator.

Today, i again checked for live data of the engine, which mostly looked correct, as far as I understand the values.

Thank you all for the inspiration. I will report ..
Whish you all a nice weekend.

 

[rockola1971]

No, i especially looked for the right temperature thermostat when i ordered it at rockauto. But the idea is good.

The radiator hint from @Fless is a hit. If there is some kind of restriction, which is missing, it would explain that behave. I would never had that idea.

But will check tomorrow the resistance of the temperature sensor for the gauge and the ecm first.

I guess the truck hat two different like in most cars, or am i wrong?

I must google tomorrow first, where the sensors are, and what resistance readings are correct, to make sure that I not search for a problem, based of wrong measured values.

If that is correct, i will check for the radiator.

Today, i again checked for live data of the engine, which mostly looked correct, as far as I understand the values.

Thank you all for the inspiration. I will report ..
Whish you all a nice weekend.

A restriction in the radiator would cause the vehicle to overheat when driven, maybe not so much at idle in a driveway. The temperature switch turns on and off the electric fans and does nothing but that. The Engine Temp Sensor tells the Instrument Cluster Temp Gauge the coolant temp as well as is also an input into the PCM for engine control. I never assume the part in the box matches the part number on the outside of the box. I just fail to see how anything other than incorrect thermostat or at the very least a stuck open thermostat would cause an engine to never get up to fully normal operating temp. Your radiator didnt become 400%+ efficient by becoming restricted or clogged up.

 

[Sam Harris]

A restriction in the radiator would cause the vehicle to overheat when driven, maybe not so much at idle in a driveway. The temperature switch turns on and off the electric fans and does nothing but that. The Engine Temp Sensor tells the Instrument Cluster Temp Gauge the coolant temp as well as is also an input into the PCM for engine control. I never assume the part in the box matches the part number on the outside of the box. I just fail to see how anything other than incorrect thermostat or at the very least a stuck open thermostat would cause an engine to never get up to fully normal operating temp. Your radiator didnt become 400%+ efficient by becoming restricted or clogged up.

Many replacement radiators are MISSING the restrictive fitting, which will cause the flow to be too great, preventing the engine from reaching the correct temperature. I am curious, but I don’t believe OP mentioned whether this had been replaced recently, or for how long he’s had this problem.

ETA: Re-reading the original post, it sounds like he’s always thought the engine wasn’t getting to normal operating temperature, so I’m guessing that rad was replaced before he acquired the rig.

 

[nonickatall]

A restriction in the radiator would cause the vehicle to overheat when driven, maybe not so much at idle in a driveway. The temperature switch turns on and off the electric fans and does nothing but that. The Engine Temp Sensor tells the Instrument Cluster Temp Gauge the coolant temp as well as is also an input into the PCM for engine control. I never assume the part in the box matches the part number on the outside of the box. I just fail to see how anything other than incorrect thermostat or at the very least a stuck open thermostat would cause an engine to never get up to fully normal operating temp. Your radiator didnt become 400%+ efficient by becoming restricted or clogged up.

I also hesitated at the beginning and said to myself, that can't be right, that's what the thermostat is there for. But after thinking about it a bit, I can already imagine it.

Because when the inner circuit heats up and the thermostat begins to open and the water flows too easily due to the lack of constriction at the outlet of the cooler - water always looks for the path of least resistance - too much cool water flows into the inner cooling circuit.

The thermostat would then close again, but would also immediately open again and the temperature would remain low.

If there was a restriction that slowed the flow through the radiator, the thermostat would have to open much further for the correct cooling effect to occur.

And what's more, the cooling escalates in two stages, because if the fully open thermostat isn't enough, the fan switches on.

As a result, I can imagine that such a lack of constriction means that the system cannot warm up properly.

Why shouldn't the engine warm up properly? This could only be because the thermostat doesn't open, but this is new and works. The old one wasn't significantly different either.

And the engine is guaranteed not to run too rich, because only these two factors could prevent it from heating up. In addition, I have so far experienced Fless as someone who knows what he is writing.

So now, as I said, I'm going to test the temperature sensors because, as I said, it's a prerequisite that the engine really isn't getting warm enough and that it's not just being displayed incorrectly to me.

And then I'll squeeze a radiator hose a little and see what happens.

Here's the question again: Does anyone know where the temperature sensors are and how many the truck has?

 

[nonickatall]

Many replacement radiators are MISSING the restrictive fitting, which will cause the flow to be too great, preventing the engine from reaching the correct temperature. I am curious, but I don’t believe OP mentioned whether this had been replaced recently, or for how long he’s had this problem.

ETA: Re-reading the original post, it sounds like he’s always thought the engine wasn’t getting to normal operating temperature, so I’m guessing that rad was replaced before he acquired the rig.

I have the problem since the beginning and i don't now if the cooler was replaced by the former owner..

 

[Fless]

A restriction in the radiator would cause the vehicle to overheat when driven, maybe not so much at idle in a driveway. The temperature switch turns on and off the electric fans and does nothing but that. The Engine Temp Sensor tells the Instrument Cluster Temp Gauge the coolant temp as well as is also an input into the PCM for engine control. I never assume the part in the box matches the part number on the outside of the box. I just fail to see how anything other than incorrect thermostat or at the very least a stuck open thermostat would cause an engine to never get up to fully normal operating temp. Your radiator didnt become 400%+ efficient by becoming restricted or clogged up.

I agree that a restriction in the radiator could cause overheating. But, to be clear, the necessary restriction I mentioned is -- or should be -- in the small hose to the surge tank. As @Sam Harris mentioned, too much flow in that hose will cause the engine temp to be low.

This short thread might help:

07 Tahoe engine hot ac turned off

So this problem has been happening for a while and I can't figure out why. First I changed the thermostat and it still happens. I changed the temperature sensor on the engine, and it still happens. I changed the wire going to the temp sensor and it still happens. Weird thing is that when I...

www.tahoeyukonforum.com

 

[nonickatall]

I agree that a restriction in the radiator could cause overheating. But, to be clear, the necessary restriction I mentioned is -- or should be -- in the small hose to the surge tank. As @Sam Harris mentioned, too much flow in that hose will cause the engine temp to be low.

This short thread might help:

07 Tahoe engine hot ac turned off

So this problem has been happening for a while and I can't figure out why. First I changed the thermostat and it still happens. I changed the temperature sensor on the engine, and it still happens. I changed the wire going to the temp sensor and it still happens. Weird thing is that when I...

www.tahoeyukonforum.com

I will check that tomorrow, for today i am done..

Disassembled a bmw diesel to find out, where the massive oil consumption comes from. Oil rings failure at 152,000 miles...

 

[rockola1971]

I agree that a restriction in the radiator could cause overheating. But, to be clear, the necessary restriction I mentioned is -- or should be -- in the small hose to the surge tank. As @Sam Harris mentioned, too much flow in that hose will cause the engine temp to be low.

This short thread might help:

07 Tahoe engine hot ac turned off

So this problem has been happening for a while and I can't figure out why. First I changed the thermostat and it still happens. I changed the temperature sensor on the engine, and it still happens. I changed the wire going to the temp sensor and it still happens. Weird thing is that when I...

www.tahoeyukonforum.com

Yup we are talking about 2 very different types of "restriction" here. You are referring to the restrictor intentionally put in the radiator inlet/outlet. Im referring to a restriction within the radiator core which is usually caused by the mixing of 2 different types of coolant and/or the permanent type getting exposed to too much air which causes it to chunk up and look like someone threw up in your radiator. Then of course using tap water full of calcium in a radiator will also do the same thing and plug the core up.

 

[nonickatall]

I agree that a restriction in the radiator could cause overheating. But, to be clear, the necessary restriction I mentioned is -- or should be -- in the small hose to the surge tank. As @Sam Harris mentioned, too much flow in that hose will cause the engine temp to be low.

This short thread might help:

07 Tahoe engine hot ac turned off

So this problem has been happening for a while and I can't figure out why. First I changed the thermostat and it still happens. I changed the temperature sensor on the engine, and it still happens. I changed the wire going to the temp sensor and it still happens. Weird thing is that when I...

www.tahoeyukonforum.com

Checked that today, I clamped the hose from radiator to the surge tank, and drove for 6 miles. I saw the temperature rise and when the thermostat opened, at above a quarter of the gauge, it dropped. Then the temperature rise, drops, rise, drops and was fluctuating between a bit over a quarter and a bit below half. When the engine was warm and stable it continued fluctuating. Then I released the clamp, to see if there is a difference. No change.

Maybe rockola1971 is right and I have a problem with my new thermostat..

What i wonder:
How our trucks react normal with engine temperature? This is my second american car and I know it from German cars like Mercedes or BMW, that temperature rise and then stay nailed in the middle of the gauge, anyway if you drive slow in winter, or 250km/h on the highway in hot summer.

I have a Chrysler LeBaron convertible and i know from many other LeBarons in our community, that the temperature fluctuates as well.

How is that on our engines? Or is that normal at American cars?

 

[adventurenali92]

Checked that today, I clamped the hose from radiator to the surge tank, and drove for 6 miles. I saw the temperature rise and when the thermostat opened, at above a quarter of the gauge, it dropped. Then the temperature rise, drops, rise, drops and was fluctuating between a bit over a quarter and a bit below half. When the engine was warm and stable it continued fluctuating. Then I released the clamp, to see if there is a difference. No change.

Maybe rockola1971 is right and I have a problem with my new thermostat..

What i wonder:
How our trucks react normal with engine temperature? This is my second american car and I know it from German cars like Mercedes or BMW, that temperature rise and then stay nailed in the middle of the gauge, anyway if you drive slow in winter, or 250km/h on the highway in hot summer.

I have a Chrysler LeBaron convertible and i know from many other LeBarons in our community, that the temperature fluctuates as well.

How is that on our engines? Or is that normal at American cars?

Under normal operation the truck will run about 200 degrees. The gauge on the dash should park at just below 210, like a hair below the 210 mark. I’ve heard a lot of guys here say that actual running temp with a scan tool hooked up will show about 199. It shouldn’t move while running especially after more than 10 or so miles depending on ambient temp. It should stay at the 210 mark on the gauge once it’s warmed up so it’s definitely not normal to see it fluctuating. The only time mines runs colder is when I’m driving down off the mountain I live on to the base area below. We have three highways in and out of town and the primary highway I use only has one little stretch of tight windy corners where I’m using a mix of throttle and letting off to get through that stretch. The majority of the highway is long sweeping corners that are properly banked where I’m doing about 50ish MPH, and when going down the truck is just coasting down the grades in 3rd gear, so it’ll drop from the 210 mark to 180ish because I’m not using enough throttle and gravity is keeping the truck moving. Unfortunately hurricane Hillary rolled through socal in late august and brought tons of rain and heavy wind that took a huge section of the highway, so it’s been closed and under repair since. With no projected opening date. So the last few trips I’ve had to take the other highway, what we refer to as the “frontside” and it’s much more windy and twisty and average speed is 35-40 MPH through most stretches. Ironically there’s longer stretches that tend to be more flat as it travels through a couple little tiny towns, and the grades are below the town. But even on that highway through several portions where the truck is just coasting through corners the temp will drop to the 180 mark. But it’ll go back up within a couple minutes of throttle to stay moving and then will stay at the correct temp.

 

[Fless]

The gauge circuit is programmed to be a bit "stupid" in that once it gets to the middle range it's not going to fluctuate much over a 10 or 20 degree range. If it did fluctuate and was highly accurate people might panic when they see it moving around. Generally the display is like @adventurenali92 stated, and remains the same indication (in the middle) over a fairly wide range of the operating temp.

 

[nonickatall]

The gauge circuit is programmed to be a bit "stupid" in that once it gets to the middle range it's not going to fluctuate much over a 10 or 20 degree range. If it did fluctuate and was highly accurate people might panic when they see it moving around. Generally the display is like @adventurenali92 stated, and remains the same indication (in the middle) over a fairly wide range of the operating temp.

Not mine...

Probably a European version?

Don't care about their feelings, just be brutally honest.

 

[afpj]

I'm starting to wonder if your propane setup just runs at a different temp and exhaust gases are different. Although your PCM is tuned for propane, are the sensors specific to propane or just regular O2 sensors? This is what we call a WAG...Wild A$$ Guess

 

[nonickatall]

I'm starting to wonder if your propane setup just runs at a different temp and exhaust gases are different. Although your PCM is tuned for propane, are the sensors specific to propane or just regular O2 sensors? This is what we call a WAG...Wild A$$ Guess

A good wild a$$ guess, well done.

But the propane system is perfect adjusted to the engine and at least it is technically very simple. The normal PCM is used, no tune at all.

The fuel injectors signal is just routed over the propane controller, and this controller decides, based on if i drive on fuel or propane, if the signal is just passed to the fuel injectors, or converted and send to to the propane nozzles. It must be converted, because the amount of propane is different to fuel, so the opening time for the propane nozzles differ from the calculated fuel injectors time.

The PCM does not know anything of the propane system, so to speak.

The PCM use the O2 Sensors, the mass air flow sensor and all other engine parameters like running on fuel. If i drive on gas, i can switch just with a push on a button to propane and opposite. My car behaves exact the same. You feel no difference.

And also the temperature behave, does not change at all.