Code 13 indicates an open in the O2 sensor circuit with the following conditions:

O2 sensor voltage is within a specified range.
Above a specified TPS value.
More than specified time after engine has warmed up.

The ECM supplies about .45 volt between terminals "9" and "14". Voltage may read as low as .32 volt when measured with a 10 megohm digital voltmeter. The O2 sensor varies the voltage within a range of about 1 volt (rich exhaust) to about .1 volt (lean exhaust).

NOTE: The following step numbers refer to the numbers in the accompanying flow chart(s).

This test checks to see if problem still exists. Normal dwell reading will vary, indicating fault is not present. Fixed dwell indicates fault.
By grounding the O2 sensor circuit to the ECM, a "low voltage (lean) signal" is sent to the ECM. This should result in a "full rich (low dwell) command" from the ECM.
This test checks O2 sensor. With the rich command, O2 sensor should read a high voltage, over .8 volt. If O2 sensor functions, fault is in sensor connections.

Fig 1: Code 13 - Open Oxygen Sensor Circuit Flow Chart

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Code 13 - Open Oxygen Sensor Circuit

Use the Manual With the Right Hardware

When to See a Mechanic

Rather have a pro handle this?