Help with Modern Electrics
Discussion
lancepar said:
What PH forum can I ask for help connecting an additional coolant temp' gauge to a car with a brain/ecu?
I'm not au fait with current electronics in vehicles
Cheers
You shouldn’t need too. I recently installed a bunch of aftermarket gauges into my car and none of them are connected to the ECU. Most gauges come with their own sender and wiring harness (if they are electrical).I'm not au fait with current electronics in vehicles
Cheers
The Autometer gauges I installed only required the following:
+12 volts switched live,
+12 volts (can be variable do dim them) that switches with the side lights or dipped beam to provide illumination,
A ground connection to the chassis
If you are wanting a decent gauge I'd get an Autometer stepper motor drive gauge, they are really nice bits of kit and require no ECU harness hacking (if you have a spare switched live in the fuse box or use an add-a-circuit piggyback (they use very little power) to get them to work.
thescamper said:
Not sure I understand why you would want an additional gauge, does the vehicle not have one fitted?
Believe it or not there is a manufacturer that decided to do away with coolant temp gauge and rely on a warning alarm/light. I have one of these and have fitted a gauge because this model of car also has a built in problem related to overheating and damaging the engine, nuf said. My gauge did come with a sensor. But as the previous model of car did have a gauge (digital) on the instrument display, my original plan, before I was told it was digital, was to tap into this wire which still exists to give an audible/light warning. I now understand I can't tap into this wire as it is Canbus, is that the correct term?
Other owners have used the OBD port but I am old school (emphasis on old).
So
The gauge is wired...red - ignition fed supply......black - earth. The green is for connecting to the sensor.
What I think I need to do is extend the green wire to the engines original sensor and tap into one of the wires from it, there's bound to be more than one.
Gauge in dash pod
So there is only one wire going to the sensor? are you sure it isn't multi-core there should be two wires for a temperature sender?
I wouldn't entertain tapping into the OEM temperature sensor wire as it will likely just be an on/off switch (thermostat) if the car isn’t fitted with a proper gauge. i.e. the warning light will come on if the temperature goes above a certain point, so here is what I would do:
Drill and tap a new sensor location in a similar area to the OE switch/sender (not knowing the anatomy of the car or engine I can’t advise on where or how you would do this) put the new sender in (use PTFE tape to seal the threads) and wire the gauge in to the appropriate supplies and to its own sender.
You are correct on not being able to physically tap into the CAN BUS, leave this well alone, though as Monty Python posted you can use a phone app and Bluetooth to read parameters from the CAN BUS. Obviously this is only useful if the sender is a sender and not a switch. The same is true for what’s called an interceptor gauge that you can buy which plugs into the OBD II port and can display any number of parameters. This however, has the same limitation as the Bluetooth app if the car is fitted with a temperature switch rather than as sender.
My car has an oil pressure gauge in the dash, it’s actually just an idiot light. If the oil pressure is above 6psi the stock sender just grounds its connection which then makes the gauge sit just to the right of centre and stays there (the stone cold oil pressure is actually around 90psi and the loaded (torque converter auto) idle is just above 20psi).
I wouldn't entertain tapping into the OEM temperature sensor wire as it will likely just be an on/off switch (thermostat) if the car isn’t fitted with a proper gauge. i.e. the warning light will come on if the temperature goes above a certain point, so here is what I would do:
Drill and tap a new sensor location in a similar area to the OE switch/sender (not knowing the anatomy of the car or engine I can’t advise on where or how you would do this) put the new sender in (use PTFE tape to seal the threads) and wire the gauge in to the appropriate supplies and to its own sender.
You are correct on not being able to physically tap into the CAN BUS, leave this well alone, though as Monty Python posted you can use a phone app and Bluetooth to read parameters from the CAN BUS. Obviously this is only useful if the sender is a sender and not a switch. The same is true for what’s called an interceptor gauge that you can buy which plugs into the OBD II port and can display any number of parameters. This however, has the same limitation as the Bluetooth app if the car is fitted with a temperature switch rather than as sender.
thescamper said:
Not sure I understand why you would want an additional gauge, does the vehicle not have one fitted?
The temperature gauge (if one is fitted) in most modern cars is normally nothing more of an extension of the usual “idiot lights” they very rarely provide a linear scale of whats happening, after all Mrs Miggins might freak out if her engine temperature went up 5 degrees (the fact the car was climbing a hill at the time and thus working harder would escaper her) and take the car back to the dealers complaining it was faulty.My car has an oil pressure gauge in the dash, it’s actually just an idiot light. If the oil pressure is above 6psi the stock sender just grounds its connection which then makes the gauge sit just to the right of centre and stays there (the stone cold oil pressure is actually around 90psi and the loaded (torque converter auto) idle is just above 20psi).
What would be useful is a wiring diagram but peeps tell me they are rarely available. It's A Mercedes/Smart thingy - top secret.
I did consider fitting the sensor that came with the gauge but prefer an easy option. The original sensor clips into the engine casing (Mitsubishi). I must have a better look and determine what wire(s) and colour(s) that come from it.
Its only a small car but fitted with all the modern bells an whistles that make messing a nightmare.
I've heard about the OBD fed gauges.
I have been using a dedicated forum for my car but their method of reminding me of my password is not working for me so I may have to register with a new user name and see if I can restore the thread on there. Hence my plea for help on here.
I understand regarding not using the output wire from the ECU, maybe if I can determine where the wire from the engine sensor goes into the ECU, I could use this as a fed to my gauge.
Cheers
I did consider fitting the sensor that came with the gauge but prefer an easy option. The original sensor clips into the engine casing (Mitsubishi). I must have a better look and determine what wire(s) and colour(s) that come from it.
Its only a small car but fitted with all the modern bells an whistles that make messing a nightmare.
I've heard about the OBD fed gauges.
I have been using a dedicated forum for my car but their method of reminding me of my password is not working for me so I may have to register with a new user name and see if I can restore the thread on there. Hence my plea for help on here.
I understand regarding not using the output wire from the ECU, maybe if I can determine where the wire from the engine sensor goes into the ECU, I could use this as a fed to my gauge.
Cheers
lancepar said:
I did consider fitting the sensor that came with the gauge but prefer an easy option.
As you're wanting to fit this to warn you of overheating, I'd be minded to prefer to fit a sensor that's completely separate from the car's existing systems - ie fit the one that came with the gauge. You won't be fooled then by the car's ECU software masking a fault. As others have pointed out, even cars that have temp gauges now often only give a reading that is generated by the ECU - it's not a true reflection of the engine temp.
Ok, here's the facts:
You engines control unit, the ECU, measures the engines coolant temperature using a std resistive sensor screwed somewhere into the cooling jacket of the engine. That sensor looks something like this:
The electrical resistance of that sensor changes with it's temperature in a known way. By feeding a current to the sensor and measuring the resultant voltage, the ECU can calculate the engines temperature. That data is used internally by the ECU to modify how the engine runs as it's temperature changes (such as running rich, or idling faster etc) and is also used to do things like turn on the radiator cooling fans when stuck in traffic etc. The temperature value is also availible on the OBD port, because EU legislation requires it to be one of the "standard OBD PIDs" that must be made availible to a scan tool or similar.
The instrument panel also receives that information, and if coolant temp goes above a certain value, illuminated the "overheating" warning lamp. Most instrument clusters also have a "cheat mode" where you can get the cluster to display data in the digital display portion of the cluster (where things like the ODO, trip counter are normally displayed)
However, you cannot just "T" into the wires that go to the sensor because the sensor is being driven by the ECU. If you put your gauge in parallel, it will also try to "drive" the sensor, and the output will be no longer correct. This is because both the engine ECU and your new Gauge have what's known as a "pull up" resistor in them. This is set to provide the correct amount of current to the temperature sensor, and so, putting two of these in parallel will mess up the output. (causing your engine ecu to read the wrong engine temperature, which is bad!)
So, either you need a "High impedance, passive" type of gauge, that just measures the voltage on the sensor without trying to drive it (you may be able to disassemble your gauge, and un-solder its internal pull up resistor). However, your gauge must be matched to the characteristic of the sensor to read correctly, which if you use the OEM sensor, it almost certainly won't be.
Some aftermarket temperature gauges can be calibrated to suit the type of sensor you are using, so this is what you would need to use if you want to use the existing temp sensor fitted to your engine.
In all cases, unless you are an electronics wiz, i'd suggest it is easier to either use an OBD port type gauge (via smart phone etc) or fit a completely seperate gauge & sensor.
You engines control unit, the ECU, measures the engines coolant temperature using a std resistive sensor screwed somewhere into the cooling jacket of the engine. That sensor looks something like this:
The electrical resistance of that sensor changes with it's temperature in a known way. By feeding a current to the sensor and measuring the resultant voltage, the ECU can calculate the engines temperature. That data is used internally by the ECU to modify how the engine runs as it's temperature changes (such as running rich, or idling faster etc) and is also used to do things like turn on the radiator cooling fans when stuck in traffic etc. The temperature value is also availible on the OBD port, because EU legislation requires it to be one of the "standard OBD PIDs" that must be made availible to a scan tool or similar.
The instrument panel also receives that information, and if coolant temp goes above a certain value, illuminated the "overheating" warning lamp. Most instrument clusters also have a "cheat mode" where you can get the cluster to display data in the digital display portion of the cluster (where things like the ODO, trip counter are normally displayed)
However, you cannot just "T" into the wires that go to the sensor because the sensor is being driven by the ECU. If you put your gauge in parallel, it will also try to "drive" the sensor, and the output will be no longer correct. This is because both the engine ECU and your new Gauge have what's known as a "pull up" resistor in them. This is set to provide the correct amount of current to the temperature sensor, and so, putting two of these in parallel will mess up the output. (causing your engine ecu to read the wrong engine temperature, which is bad!)
So, either you need a "High impedance, passive" type of gauge, that just measures the voltage on the sensor without trying to drive it (you may be able to disassemble your gauge, and un-solder its internal pull up resistor). However, your gauge must be matched to the characteristic of the sensor to read correctly, which if you use the OEM sensor, it almost certainly won't be.
Some aftermarket temperature gauges can be calibrated to suit the type of sensor you are using, so this is what you would need to use if you want to use the existing temp sensor fitted to your engine.
In all cases, unless you are an electronics wiz, i'd suggest it is easier to either use an OBD port type gauge (via smart phone etc) or fit a completely seperate gauge & sensor.
The car has an overheat light test function when the ignition is switched on.
This model of car has an alternator/starter in one unit, good idea up to now. A poly belt goes on the pulley of this unit to the crankshaft and the water pump pulleys. If the belt snaps the warning of overheat and battery excite lamp comes on the dash (not sure if there is an audible as well). If the engine is switched off immediately as it should be then the engine can be saved (it can't be restarted obviously but one might be tempted to continue to a safe place to stop).
I was hoping an aftermarket gauge could be simply added to show a rise in temperate (like the 2007 model did), the gauge I bought also has a red 100C warning light as well as its number display, see my pic it starts at 40C.
Max Torque.....I posted this then saw you message, I understand how the original sensor works now, thanks
This model of car has an alternator/starter in one unit, good idea up to now. A poly belt goes on the pulley of this unit to the crankshaft and the water pump pulleys. If the belt snaps the warning of overheat and battery excite lamp comes on the dash (not sure if there is an audible as well). If the engine is switched off immediately as it should be then the engine can be saved (it can't be restarted obviously but one might be tempted to continue to a safe place to stop).
I was hoping an aftermarket gauge could be simply added to show a rise in temperate (like the 2007 model did), the gauge I bought also has a red 100C warning light as well as its number display, see my pic it starts at 40C.
Max Torque.....I posted this then saw you message, I understand how the original sensor works now, thanks
Edited by lancepar on Wednesday 19th November 15:23
Edited by lancepar on Wednesday 19th November 15:24
Max_Torque said:
Ok, here's the facts:
You engines control unit, the ECU, measures the engines coolant temperature using a std resistive sensor screwed somewhere into the cooling jacket of the engine. That sensor looks something like this:
The electrical resistance of that sensor changes with it's temperature in a known way. By feeding a current to the sensor and measuring the resultant voltage, the ECU can calculate the engines temperature. That data is used internally by the ECU to modify how the engine runs as it's temperature changes (such as running rich, or idling faster etc) and is also used to do things like turn on the radiator cooling fans when stuck in traffic etc. The temperature value is also availible on the OBD port, because EU legislation requires it to be one of the "standard OBD PIDs" that must be made availible to a scan tool or similar.
The instrument panel also receives that information, and if coolant temp goes above a certain value, illuminated the "overheating" warning lamp. Most instrument clusters also have a "cheat mode" where you can get the cluster to display data in the digital display portion of the cluster (where things like the ODO, trip counter are normally displayed)
However, you cannot just "T" into the wires that go to the sensor because the sensor is being driven by the ECU. If you put your gauge in parallel, it will also try to "drive" the sensor, and the output will be no longer correct. This is because both the engine ECU and your new Gauge have what's known as a "pull up" resistor in them. This is set to provide the correct amount of current to the temperature sensor, and so, putting two of these in parallel will mess up the output. (causing your engine ecu to read the wrong engine temperature, which is bad!)
So, either you need a "High impedance, passive" type of gauge, that just measures the voltage on the sensor without trying to drive it (you may be able to disassemble your gauge, and un-solder its internal pull up resistor). However, your gauge must be matched to the characteristic of the sensor to read correctly, which if you use the OEM sensor, it almost certainly won't be.
Some aftermarket temperature gauges can be calibrated to suit the type of sensor you are using, so this is what you would need to use if you want to use the existing temp sensor fitted to your engine.
In all cases, unless you are an electronics wiz, i'd suggest it is easier to either use an OBD port type gauge (via smart phone etc) or fit a completely seperate gauge & sensor.
^^^^You engines control unit, the ECU, measures the engines coolant temperature using a std resistive sensor screwed somewhere into the cooling jacket of the engine. That sensor looks something like this:
The electrical resistance of that sensor changes with it's temperature in a known way. By feeding a current to the sensor and measuring the resultant voltage, the ECU can calculate the engines temperature. That data is used internally by the ECU to modify how the engine runs as it's temperature changes (such as running rich, or idling faster etc) and is also used to do things like turn on the radiator cooling fans when stuck in traffic etc. The temperature value is also availible on the OBD port, because EU legislation requires it to be one of the "standard OBD PIDs" that must be made availible to a scan tool or similar.
The instrument panel also receives that information, and if coolant temp goes above a certain value, illuminated the "overheating" warning lamp. Most instrument clusters also have a "cheat mode" where you can get the cluster to display data in the digital display portion of the cluster (where things like the ODO, trip counter are normally displayed)
However, you cannot just "T" into the wires that go to the sensor because the sensor is being driven by the ECU. If you put your gauge in parallel, it will also try to "drive" the sensor, and the output will be no longer correct. This is because both the engine ECU and your new Gauge have what's known as a "pull up" resistor in them. This is set to provide the correct amount of current to the temperature sensor, and so, putting two of these in parallel will mess up the output. (causing your engine ecu to read the wrong engine temperature, which is bad!)
So, either you need a "High impedance, passive" type of gauge, that just measures the voltage on the sensor without trying to drive it (you may be able to disassemble your gauge, and un-solder its internal pull up resistor). However, your gauge must be matched to the characteristic of the sensor to read correctly, which if you use the OEM sensor, it almost certainly won't be.
Some aftermarket temperature gauges can be calibrated to suit the type of sensor you are using, so this is what you would need to use if you want to use the existing temp sensor fitted to your engine.
In all cases, unless you are an electronics wiz, i'd suggest it is easier to either use an OBD port type gauge (via smart phone etc) or fit a completely seperate gauge & sensor.
You wanted the easy route and that is imho to use the sensor that came with the gauge.
Because the other option for the temperature sensor is simply a switch that turns the warning light on at a certain temperature (like the oil pressure switch on my car). That has no proportional output like the sensor above. It either has infinite resistance or no resistance which means the gauge will read its maximum or minimum value so you couldn't use that either.
The gauge has a sensor supplied with it because that is the easy option!
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