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Coolant Temperature and Oil Pressure Sensor Replacement
 
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Pelican Technical Article:

Coolant Temperature and Oil Pressure Sensor Replacement

Nick Czerula

Time:

3 hour3 hr

Tab:

$100

Talent:

***

Tools:

25mm socket, flathead screwdriver

Applicable Models:

BMW Z4 Coupe/Conv (2006)

Parts Required:

Oil pressure sensor or coolant temperature sensor

Hot Tip:

Work with a cool engine

Performance Gain:

Remedy gauge issues or fault codes

Complementary Modification:

Replace engine oil or engine coolant

The coolant temperature sensor is a resistor that has a negative temperature coefficient (NTC). This means that the resistance decreases as temperature increases. The resistor is part of a voltage divider circuit that receives 5 volts from the DME. The voltage signal changes depending on engine coolant temperature. The sensor is located on a coolant pipe at the left front side of the cylinder head.

There is a table stored in the DME that specifies the corresponding temperature to each voltage value and therefore compensates the non-linear correlation between voltage and temperature. The resistance changes dependent on temperature from 167 k Ohms to 150 Ohms, corresponding to a temperature from -40 degrees C to 130 degrees C.

The oil pressure sensor (switch) is located on the rear of the oil filter housing. It consists of a switch, which closes when oil pressure in the engine falls below 0.2 bar (3 psi). When this circuit is closed an output in the instrument cluster is grounded, and the warning lamp is illuminated.

When an oil pressure sensor fails, the engine oil pressure light will illuminate or not come on with the key on and engine off. I have seen low engine oil pressure cause similar problems to a sensor, so be sure to test engine oil pressure if you suspect it may be low, especially if you have a flickering oil pressure light.

The oil pressure switch signal is connected to the DME. When the switch is activated 12 volts is sent to the DME. When the switch is not activated 0 volts is sent to the DME.

Oil Pressure Specification

800 rpm: 0.7 bar (10 psi)

3000 rpm - 4.0 bar (43.5 psi)

NOTE: Oil pressures apply at an oil temperature of 100 degrees C, which is reached after 10-15 minutes of driving.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability.

Vehicle models change and evolve, as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

In this article, I'll go over the steps involved with replacing the oil pressure sensor and the coolant temperature sensor on a BMW Z4 with a S54 6-cylinder engine. Other engines are similar. Start by removing the intake manifold. This is the easiest way to access and replace both sensors. See our tech article on intake manifold replacing. Drain the engine coolant if you're replacing the coolant sensor.

The coolant temperature sensor is a resistor that has a negative temperature coefficient (NTC).
Figure 1

The coolant temperature sensor is a resistor that has a negative temperature coefficient (NTC). This means that the resistance decreases as temperature increases. The resistor is part of a voltage divider circuit that receives 5 volts from the DME. The voltage signal changes depending on the engine coolant temperature. The sensor is located on a coolant pipe at the left front side of the cylinder head (green arrow points to area with engine assembled). The oil pressure sensor (switch) is located on the rear of the oil filter housing (red arrow points to area with engine assembled). It consists of a switch, which closes when oil pressure in the engine falls below 0.2 bar (3 psi). When this circuit is closed an output in the instrument cluster is grounded and the warning lamp is illuminated.

The sensor is located on a coolant pipe at the left front side of the cylinder head (green arrow).
Figure 2

The sensor is located on a coolant pipe at the left front side of the cylinder head (green arrow). The oil pressure sensor (switch) is located on the rear of the oil filter housing (red arrow). It consists of a switch, which closes when oil pressure in the engine falls below 0.2 bar (3 psi). When this circuit is closed an output in the instrument cluster is grounded and the warning lamp is illuminated.

Oil pressure sensor: Start by disconnecting the oil pressure sensor electrical connector.
Figure 3

Oil pressure sensor: Start by disconnecting the oil pressure sensor electrical connector. Press the wire retainer (yellow arrow) and pull the connector straight off.

Oil pressure sensor: Loosen the oil pressure sensor (red arrow).
Figure 4

Oil pressure sensor: Loosen the oil pressure sensor (red arrow). Use a 24mm wrench.

Oil pressure sensor: Then unscrew the sensor by hand (red arrow).
Figure 5

Oil pressure sensor: Then unscrew the sensor by hand (red arrow).

Oil pressure sensor: Be sure to replace the sealing washer (green arrow) when installing the sensor again after testing or when installing a new sensor.
Figure 6

Oil pressure sensor: Be sure to replace the sealing washer (green arrow) when installing the sensor again after testing or when installing a new sensor. Top up the engine oil level when done. Reassemble the engine components.

Coolant sensor: Start by disconnecting the idle air control valve electrical connector.
Figure 7

Coolant sensor: Start by disconnecting the idle air control valve electrical connector. Press the wire retainer (red arrow) and pull the connector straight off.

Coolant sensor: On my subject vehicle the coolant temp sensor electrical connector was positioned in a way that I could not access the wire retainer (green arrow).
Figure 8

Coolant sensor: On my subject vehicle the coolant temp sensor electrical connector was positioned in a way that I could not access the wire retainer (green arrow). To make getting to it easier, I loosened the sensor using a 22mm wrench (red arrow).

Coolant sensor: Next, rotate the sensor around to disconnect the electrical connector.
Figure 9

Coolant sensor: Next, rotate the sensor around to disconnect the electrical connector. Press the wire retainer (red arrow) and pull the connector straight off.

Coolant sensor: Remove the sensor from the coolant pipe.
Figure 10

Coolant sensor: Remove the sensor from the coolant pipe. Be sure to replace the sealing washer (green arrow) when installing the sensor again after testing or when installing a new sensor. Top up the engine coolant level when done. Reassemble the engine components.

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Page last updated: Fri 12/2/2016 02:57:02 AM