Boost Air Temperature Sensor fault?

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dieselonly

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10
Hello, i get weird reading from Boost Air Temp sensor. After cold startup it is around 120*C and value is not constant, changes from 117*C to 121*C on idle.

I've mistaken Intake Air Temp sensor and replaced one that's installed in boost pipe, wrong sensor replaced i guess.

Can somebody confirm that Boost Air Temperature sensor is that one integrated into MAF sensor installed at airbox?

2004 TD4 Freelander 1, 204D3 M47R diesel engine.
 
The boost air temperature sensor is in the boost hose at the front of the engine.
The intake air temperature sensor is part of the MAF.
 
So i've replaced good one. Both old and new have same behavior, so it is wiring problem?
120*C is a bit too much for cold startup i guess :) Wiring or what?

Both old and new sensors change values on live data slightly so there is no fault codes stored untill disconnected.
Cold start at 10*C ambient, Boost air temp started from 117*C and raised to 121*C within 5 minutes:

2024_01_03_17_26_page-0001.jpg


I got 5V voltage supply to sensor and resistance on the sensor itself measured at 0.3 - 0.4 Ohm @ 10*C ambient.

What to do next?
 
Last edited:
Is the intercooler core clogged with mud or flies? If not it could be a read error on the reader, which I've seen before. I'd not expect to see a boosted air temperature above 50°C, maybe slightly more if its a hot day.
 
IC is clean outside and clean enough inside. I do check silicone hoses for oil/carbon and they are very clean. IC is ice cold and hoses also cold, impossible to get 120*C at all.

How i can measure signal coming out from this sensor using multimeter?
How to check continuity on the wire itself? Which pin on ECU?
 
dieselonly said:
IC is clean outside and clean enough inside. I do check silicone hoses for oil/carbon and they are very clean. IC is ice cold and hoses also cold, impossible to get 120*C at all.

How i can measure signal coming out from this sensor using multimeter?
How to check continuity on the wire itself? Which pin on ECU?
Click to expand...
There are 2 wires at the sensor, but they're very likely to break, often disappearing altogether.
 
It must be software issue with reading value for boost air temperature.
I got 5V on connector, after a week and 300km later there is no fault codes.

To confirm software issue we should ask @pscan.eu what is the value of this reading after plug is disconnected.
When the sensor is disconnected or broken, DS150 clone with any compatible software will show constant 128.9*C which can't be real value for broken sensor.

Intercooler is cold, 5V on connector, low resistance on sensor, no fault codes, value is ridiculously high but it's changing - must be software issue.
 
dieselonly said:
It must be software issue with reading value for boost air temperature.
I got 5V on connector, after a week and 300km later there is no fault codes.

To confirm software issue we should ask @pscan.eu what is the value of this reading after plug is disconnected.
When the sensor is disconnected or broken, DS150 clone with any compatible software will show constant 128.9*C which can't be real value for broken sensor.

Intercooler is cold, 5V on connector, low resistance on sensor, no fault codes, value is ridiculously high but it's changing - must be software issue.
Click to expand...
Thanks did you ever find the correct ECU pins for the sensor
 
325andy said:
Thanks I will test that and see
Click to expand...
Hi I located the pins on the ECU to run new wires but still with the same readings, is your car running ok with the high temp reading, I have a boost air temp reading of 120 C on idle with a cold engine and 0.0mV sensor reading.
 
I wouldn't be worrying about it. The early models didn't even use the boosted temp sensor.
Have you checked that the VIN on the ECM is correct for your car? It's not inconceivable that the ECM has been replaced with an early one, which doesn't know that sensor is even there.
 
Nodge68 said:
I wouldn't be worrying about it. The early models didn't even use the boosted temp sensor.
Have you checked that the VIN on the ECM is correct for your car? It's not inconceivable that the ECM has been replaced with an early one, which doesn't know that sensor is even there.
Click to expand...
I will check that, but something is wrong as the car is over fuelling on anything over 2000 revs, runs well on idle I will have to keep looking.
 
Over fueling is normal due to low boost pressure. The ECM can only fuel up to a set rate. If that fuel rate is too much for the air available, then there's a problem with air supply, or the exhaust getting out again.
The boosted air sense only makes tiny adjustments in fueling, not enough to prevent over fueling issues. A diesel is throttled by fuel, so too much fuel and no increase in power means not enough air to burn the fuel.
 
Nodge68 said:
Over fueling is normal due to low boost pressure. The ECM can only fuel up to a set rate. If that fuel rate is too much for the air available, then there's a problem with air supply, or the exhaust getting out again.
The boosted air sense only makes tiny adjustments in fueling, not enough to prevent over fueling issues. A diesel is throttled by fuel, so too much fuel and no increase in power means not enough air to burn the fuel.
Click to expand...
That all makes sense, given me lots to think about Thanks
 
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