Oxygen Sensor Heaters, Checking

The following procedure is used to diagnose Oxygen Sensor (O2S) Heater -Z19- for Heated Oxygen Sensor (HO2S) -G39- and Oxygen Sensor (O2S) 2 Heater -Z28- for Heated Oxygen Sensor (HO2S) 2 -G108-.

Special tools and workshop equipment required 

• Multimeter.
• Wiring diagram.

Test requirements

• The Oxygen Sensor (O2S) Heater -Z19- for Heated Oxygen Sensor (HO2S) -G39- and Oxygen Sensor (O2S) 2 Heater -Z28- for Heated Oxygen Sensor (HO2S) 2 -G108- fuses OK.
• Battery voltage at least 12.5 volts.
• All electrical consumers such as, lights and rear window defroster, switched off.
• Vehicles with automatic transmission, shift selector lever into position "P" or "N".
• A/C switched off.
• Ground (GND) connections between engine/transmission/chassis OK.
• Ignition switched off.

Test procedure

-- Perform a preliminary check to verify the customers complaint. Refer to GENERAL DIAGNOSIS .

Start diagnosis

-- Remove the engine cover with air filter.

Checking internal resistance

-- Disconnect the Heated Oxygen Sensor (HO2S) -G39- electrical harness connector -2- or the Heated Oxygen Sensor (HO2S) 2 -G108- electrical harness connector -1-.

-- Using a multimeter, check the Heated Oxygen Sensor (HO2S) -- terminals 3 to 4 for an open circuit.

Specified value: 2.5 to 10.0 Ω (at approx. 20° C)

If the specification was not obtained:

-- Replace the 2- Heated Oxygen Sensor (HO2S) -G39- or the 1- Heated Oxygen Sensor (HO2S) 2 -G108-.

If the specification was obtained:

Checking voltage supply

-- Using a multimeter, check the Heated Oxygen Sensor (HO2S) -- electrical harness connector terminal 4 to theFuel Pump (FP) 2 Relay -J49- terminal 2/87 for voltage.

Heated Oxygen Sensor (HO2S) -G39- and Heated Oxygen Sensor (HO2S) 2 -G108- electrical harness connector terminal	Fuel Pump (FP) 2 Relay -J49- electrical harness connector terminal
4	2/87

Specified value: Battery voltage.

If the specification was not obtained:

-- Check the wiring for a short circuit to each other, Battery (+), and Ground (GND).

-- Check the electrical harness connector for damage, corrosion, lose or broken terminals.

-- If necessary, repair the faulty wiring connection.

If the specification was obtained:

Checking Ground (GND) activation

If the manufacturers test box is being used. Perform the following step.

-- Install the test box. Refer to Repair information.

If the manufacturers test box is not being used. Perform the following step.

-- Remove the Motronic Engine Control Module (ECM) -J220-. Refer to MOTRONIC ENGINE CONTROL MODULE, REPLACING .

-- Using a multimeter, check the Heated Oxygen Sensor (HO2S) -- electrical harness connector to the Motronic Engine Control Module (ECM) -J220- electrical harness connector T121 for an open circuit.

Heated Oxygen Sensor (HO2S) -G39- electrical harness connector terminal	Motronic Engine Control Module (ECM) -J220- electrical connector T121 terminal or test box socket
3	5

Heated Oxygen Sensor (HO2S) 2 -G108- electrical harness connector terminal	Motronic Engine Control Module (ECM) -J220- electrical connector T121 terminal or test box socket
3	4

Specified value: 1.5 Ω max.

If the specification was not obtained:

-- Check the wiring for a short circuit to each other, Battery (+), and Ground (GND).

-- Check the electrical harness connector for damage, corrosion, lose or broken terminals.

-- If necessary, repair the faulty wiring connection.

If no malfunction is detected in the wiring and if the voltage supply was OK:

-- Replace the Motronic Engine Control Module (ECM) -J220-. Refer to MOTRONIC ENGINE CONTROL MODULE, REPLACING .

-- Install the engine cover with air filter.

Final procedures

After repair work, the following work steps must be performed in the following sequence:

1. Check the DTC memory. Refer to DIAGNOSTIC MODE 03 - READ DTC MEMORY .
2. If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
3. If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .

-- End of diagnosis.