Frequently Asked Question
Background: One side of the OAT probe connects to ground, and the other to the OAT input of the EIS. If either of these connections is open, the EIS will show -50 F.
Cause: Open circuit.
- The connection from the EIS to the OAT probe is open, or
- The OAT connection to ground is open, or
- The OAT probe is failed open.
Troubleshooting:
- A simple way to check for a good OAT probe and the wiring is to disconnect the connector from the EIS, and measure the resistance from the OAT/Carb temperature probe, to ground. The reading should be less than 50k ohms, and is typically 10k ohms at 77 deg F. If open, check the probe and wiring. The probe should measure less than 50k ohms between its leads.
To see if the connection to the EIS is good:
Troubleshooting without a voltmeter: Turn on the EIS. Locate the connection connection between the EIS and the OAT probe. Short this connection to ground. (It is not necessary to disconnect the OAT probe for this test.) The EIS should read a very high value (above 120 F). If the reading does not change, the connection to the EIS is open. The open may be at the d-sub connector, or the wire to the EIS may be broken.
Troubleshooting using a voltmeter: To determine if the connection to the EIS is good, turn on the EIS, and with the OAT probe connected, measure the voltage at the point where the EIS OAT input connects to the OAT probe. If this voltage is very close to 5V (greater than 4.5V), the probe is bad or its connection to ground is open. If this voltage is zero, the connection to the EIS is open.
To see if the OAT/Carb Ground connection is good:
Using a voltmeter, connect on lead to a known good ground (such as the negative terminal of the battery), and the other lead to the point where the probe connects to ground. With the EIS turned on, the voltmeter should read very close to zero volts (less than 0.05 or 50 mV). If the voltmeter reads about 5V, the ground connection the probe is using is not a good ground.
To see if the OAT/Carb probe is good:
Disconnect one or both of its leads. Measure the resistance between the two leads using a volt-ohm meter set to OHMS. At room temperature the reading should be in the range of 5k-15k (5000 – 15,000) ohms. If the reading is a short (near zero ohms) or an open, the probe is bad.