Electrical: Engine Sensors PDF
FAQ Home
Volvo Maintenance FAQ for 7xx/9xx/90 Cars
Engine Temperature Sensors. The B230F of the vintage discussed, 1989-1995 have in effect three temp sensors. The Temperature Gauge Sensor is at the front under intake manifold runner number two, just ahead of the knock sensor which is bolted in at an angle. It has two round pin connectors, one signal, one ground. For resistance ratings, see the link noted. Behind the knock sensor under manifold runner three is the Engine Coolant Temperature Sensor - ECT -which is in effect two sensors in one housing. Two NTC thermistors are combined in one ECT sensor housing with two flat connectors and ground through the housing into the manifold. One of the temp sensor signals goes to the LH fuel injection computer, the other to the EZK ignition computer. When you remove any of the sensors, disconnect the battery negative cable.
Removing the Sensors.
Do I Need to Drain the Coolant? [John Mc] Release any residual pressure in the system by opening the cap, then close it again. Get the old ECT loose, get the new one ready to go, then just pop the old one out and put the new one in as quickly as possible. You really won't lose very much coolant at all. The sealed system will glug out a little bit, then build a slight vacuum and stop. Put the new one in, tighten, then rinse away the slight leakage with a hose and top off the missing pint or less.
Gauge Temperature Sensor. [Inquiry] How do I remove the gauge temperature sensor? Gauge Temperature Sensor[Mark Duval] This is the front sensor under intake manifold runner number two with the two round pins. A 19mm socket will not work because of the width of the wiring connector. I bought the stubby 19mm combination wrench and a 19mm crow foot socket. First tried the open end side of the stubby and although I could get it squarely on the hex head, I could not put enough force on the wrench to turn the sensor. Then used the crow foot socket with a long extension. This rotated off the hex and cracked the electrical connection at the top of the sensor. The answer all along was to remove the sensor's molded-on electrical connector (destroying the sensor) and gain access to the hex with an offset 19mm box wrench or a 3/4 inch socket. [Jay Simkin] Remove the old sensor and prep the new sensor by applying a thin coat of grease on the threads. Then apply grey pipe joint compound (not the white, teflon-loaded joint compound) in a collar of compound on the underside of the sensor's lip, above the threads. Keep the joint compound away from the threads. To reinstall, gently screw the prepped sensor into the opening in the block. Tighten snug using a 3/4" open end wrench. A 3/4" socket will not work, as the electrical connector housing is wider than the brass hex fitting used to secure the sensor. Check for leaks. Tighten gently if required to stop any leaks. Replace the knock sensor using a 12mm wrench to tighten it securely against the engine block. Replace both electrical connectors and reconnect the battery negative.
[Editor] It helps to first remove assorted tubes and pipes, including the IAC valve and the knock sensor nearby, which is merely bolted into the block.
Fuel Injection Coolant Temperature SensorEngine Coolant Temperature Sensor. Removing the Engine Coolant Temperature Sensor (the rear-most of the three sensors, Volvo p/n 1346030 or Bosch 0280130032) is a little tougher, since it is buried under intake manifold runner number three. Two contrary removal tips: [Tip from John Sargent] Removing the intake manifold makes it less than a 30 minute job. Trying to R&R without removing the intake manifold can lead to a broken sensor. The brass hex of the ECT is 19mm. The electrical connector is larger than the 19mm hex and a socket or box end wrench will not fit over the electrical connector, so you can only use an open end wrench to remove the ECT. The wiring harness connector can be very difficult to disconnect without removing the intake manifold. Save yourself on both aggravations, just get an intake manifold gasket if the sensor needs to be replaced. [Jay Simkin] This sensor's wiring connector housing fits inside a 19mm deep socket, which then engages the sensor's brass hex fitting. I recently did this job, and used a 3/8" 19mm deep socket to remove the sensor from the head. There was just enough work room between the manifold's runners (I have small hands). I put the socket on the sensor, and then inserted the ratchet's square protrusion into the socket. By contrast, the temperature gauge's coolant sensor (towards the front of the head) has a wiring connector housing wider than is the sensor's brass hex fitting. Therefore, some may need to remove the connector housing, before removing the sensor.
Installing the Sensors. [Editor] Do NOT use Teflon tape or Teflon pipe sealer on the threads when reinstalling since they may interfere with temperature readings and with grounding against the block. Better to use thin coat of a conductive grease such as OxGard or apply pipe joint compound above the threaded area.
Diagnosing ECT Failures. [Response: Don Foster, adapted to 700/900 series by Editor] Your engine has two temp sensors -- one for the gauge (it's mounted in the head about under intake header #2, and one for the FI (it's mounted in the head about under intake header #3). The latter is the ECT sensor.
The sensor is an NTC thermistor -- negative temperature coefficient. As the temp drops, the resistance rises, and as the temperature rises, the resistance drops. Thus, if you have a broken wire, defective sensor, or bad connection (I've seen it happen) the resistance measured by the ecu will be very high or infinite. The ECU interprets this as minus a zillion degrees and pours in the gas
The car I saw filled the oil with gas and certainly wouldn't run. And the problem was only a displaced spade lug in the plastic connector housing. According to Chilton's (you may choose to disregard this):
The coolant temperature signal to the control unit has a great influence on the computed injection period... For example, when the engine is being started and is cold, the amount of injected fuel must be relatively large. [Editor:] Too rich a mixture because of a failing ECT may lead to idle surges, high idle, poor warm running, or other symptoms of too much fuel. See Engine Tune and Performance; Symptoms for more examples.
If the control unit receives a signal higher than 302F (150C) or lower than -40F (-40C), it will interpret the signal as a fault...the control unit will assume a substitute value corresponding to 32F (0C) on starting and 68F (20C) when the engine has started.
With the control unit connected, connect a voltmeter across LH ECU terminals 13 and 5 (ground) for Bosch LH 2.4 systems or terminals 2 and 5 (ground) for LH 2.2 systems. This unit is in the passenger side footwell, under the plastic cover. Remove the cover of the large electrical connector to access the backs of the pins for the test. Turn the ignition switch ON.
At 68F (20C) the voltage should be 2.0 +/-.5v volts.
At 104F(40C) the voltage should be 1.2 +/- .3volts
At 176F (80C) the voltage should be .5 +/- .2volts.
The resistance values between ECU pins 13 and 5, or between each of the pins on the sensor and ground, are (by eye from the chart):
32F (0C)-- about 6000 ohms within a range of +/- 10%
68F(20C) -- about 2300 ohms
104F(40C) -- about 1300 ohms
140F(60C) -- about 600 ohms
176F(80C) -- about 300 ohms
212F -- about 190 ohms
[Response: Steve Ringlee] ECT resistance cold for LH2.4 systems should be around 6k ohms at 32 degrees F (0 deg C), 2300-2700 ohms at 68 degrees F (20 C), and 200 at 212 F (100 C). However, try checking your ECT wiring: Between pins 13 and 5 at the LH ECU (with sensor DISconnected) resistance should be infinite. Voltage with the ignition ON and sensor connected, measured between pins 13 and 5, should be:
0 C=around 3 volts +/-.5v
20C=around 2 volts +/- .5v
100C=around .3 volt +/- .1v
If these aren't correct, check the connections in the ECT wiring harness. Check engine ground connections at the intake manifold. If the voltage is zero, your ECU is at fault.
