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Discussion Starter · #1 ·
I have tried getting an ohm reading on my engine coolant temperature sensor (the one under the green connector) when the engine is full hot and get strange or no readings. I'm either getting no reading at all or a reading that jumps around. I have tried several digital volt/ohmeters and they all do the same thing. Had a friend, who is a former tech, check it with his meter and he got the same thing. The prongs to the sensor are clean, so that's not an issue. Cold I can get a reading. Can anyone with a 5SFE engine try to read their sensor when the engine is full hot and let me know what reading you get. You need to set the meter to a 20,000 ohm scale.

Thanks in advance for the help.

Mike
 

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Ninja wrench anywhere
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Why are you on 20,000ohm scale? That sensor is only like 200ohms when the coolant's at operating temperature.
 

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Discussion Starter · #4 ·
Looking for a little help here. Can anybody with a meter and a 5SFE engine give me an ohm reading on their engine coolant temp sensor on a hot engine?

Mike
 

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Looking for a little help here. Can anybody with a meter and a 5SFE engine give me an ohm reading on their engine coolant temp sensor on a hot engine?

Mike
Can get you the numbers tomorrow - will check back.

Thanks for your past help and comments.
 
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Mine read 245 ohms at normal operating temp. If your reading is jumping around, the resistor may be trying to go open circuit at normal temp. Has your gas mileage been affected? What range is it jumping around in? Here's a graph in case you need to compare for a cold reading as well.

 

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Discussion Starter · #9 ·
"Mine read 245 ohms at normal operating temp. If your reading is jumping around, the resistor may be trying to go open circuit at normal temp. Has your gas mileage been affected? What range is it jumping around in?"

My gas mileage hasn't been affected. My reading was jumping from 2,214 ohms to around 200 ohms. Sometimes I would get no reading at all. That may have been because I had the meter set to a 20,000 ohm scale, as hill8570 pointed out. I still think my reading is high on a cold engine, but OK on the warm side. It will probably be OK until next fall. The car always starts, no matter how cold it is. It's just that there is no fast idle in cold weather until I tap the gas pedal and then it shoots up to 1200 RPM, as if I'm clearing out an overly rich mixture. My cold engine readings were 6,150 ohms at 34 degrees F, 5,650 ohms at 41 degrees F, and 3,110 ohms at 67 degrees F. I think these are a bit high, so i was trying to see if my readings were normal on a warm engine. There are no codes present, but I really wouldn't expect a code for this on an OBD1 sytem, unless the sensor had a dead short or didn't give a reading at all.

Thanks for the reading.

Mike
 

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Mike, my FSM gives a graph with a high and low range of acceptable readings at a particular temp - 212* F shows about .2K ohms to .3K ohms. There are not even any grid lines on the graph so I'm thinking it's not that critical. If you want the graph PM me and I'll scan and email.
 

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Discussion Starter · #11 ·
Mike, my FSM gives a graph with a high and low range of acceptable readings at a particular temp - 212* F shows about .2K ohms to .3K ohms. There are not even any grid lines on the graph so I'm thinking it's not that critical. If you want the graph PM me and I'll scan and email.
I have the FSM myself and saw that graph, but it seemed like a quite a range at the low end. That's why I wanted to get real world readings on other people's 5SFE coolant temp sensors. Thanks for the thought.

Mike
 

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My gas mileage hasn't been affected. My reading was jumping from 2,214 ohms to around 200 ohms. Sometimes I would get no reading at all. That may have been because I had the meter set to a 20,000 ohm scale, as hill8570 pointed out. I still think my reading is high on a cold engine, but OK on the warm side. It will probably be OK until next fall. The car always starts, no matter how cold it is. It's just that there is no fast idle in cold weather until I tap the gas pedal and then it shoots up to 1200 RPM, as if I'm clearing out an overly rich mixture. My cold engine readings were 6,150 ohms at 34 degrees F, 5,650 ohms at 41 degrees F, and 3,110 ohms at 67 degrees F. I think these are a bit high, so i was trying to see if my readings were normal on a warm engine. There are no codes present, but I really wouldn't expect a code for this on an OBD1 sytem, unless the sensor had a dead short or didn't give a reading at all.
Those resistance numbers all look pretty reasonable to me (other than the jumping around when warmed up).

Have you checked out your Idle Air Control (IAC) valve? You'll get low cold idle if it isn't opening on cold start. Quick way to check it is to jumper TE1 and E1 (with ye olde unbent paperclip) on DLC1 (the test connector up near the passenger side firewall) while the car is running warm. If the IAC more-or-less OK, idle rpms will jump above 1000 for a couple seconds before setting back down in the 750 range.
 

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Discussion Starter · #13 · (Edited)
I haven't run the test on the idle air control valve. It is always cleaned while cleaning the throttle body once or twice a year. Since I only have to tap the gas pedal once after a cold winter start to raise the idle to around 1200, logic tells me that if the valve wasn't working I wouldn't get any fast idle. I posed this question to a former Lexus tech I know, and he said that since I get a fast idle, then the idle air control valve is working. Also, the car has never died or dropped way down when at idle at a stop with a warm engine. That usually happens when the idle air control valve isn't working or is dirty. I still think my cold readings are a bit high, which could be causing the rich cold start idle mixture that I think I am getting. I got 6,150 ohms at 34 degrees F, where I think it should be around 4,000 ohms.

Mike
 

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See you got some pretty good info already.

2.5K to 3K ohms at 68 F (room temp - cold) - it'll be higher in colder weather.

250 to 300 ohms at 180 F (near to operating temp).

You should also check each terminal to the block, it should be infinite Meg ohms, with the connector off and measuring directly to the sensor terminals.

You can substitute a fixed resistor for the sensor on the plug connections.

Let your car warm up and measure the sensor terminals again while disconnected. It should be a constant resistance, it should not jump around. If it does it should be replaced as it has an internal fault.
 

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In general, the radiator fan switch is usually on the bottom plastic tank of the radiator. The coolant temperature sensor is usually near the engine coolant outlet (upper radiator hose).

Detail info you can probably get from Autozone's free repair guide (with registration). http://www.autozone.com/autozone/repairinfo/repairInfoLanding.jsp

You can also look up what the parts look like on rockauto.com



can anyone tell me where to find the coolant emperature sensor and radiator fan switch on a 94 tercel?
 
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