2003 Mercury Grand Marquis OBD2 Code P0043 HO2S Heater Control Circuit Low (Bank 1 Sensor 3)

P0043 code definition

P0043 stands for low circuit voltage for the heated oxygen sensor bank 1 sensor 3. This code can be seen with P0044 and P0042.

What the P0043 code means

The definition of P0043 is low voltage for the heater control circuit. P0043 indicates that the car's ECU has detected lower than expected voltage and has triggered a warning light.

What causes the P0043 code?

P0043 may have a few typical causes:

• Bank 1 sensor 3 has failed
• Open or shorted wiring for bank 1 sensor 3
• Poor electrical connection or high resistance
• Internal ECU issues

What are the symptoms of the P0043 code?

The 2003 Mercury Grand Marquis 's engine control unit (ECU) detects lower than specified voltage from bank 1 sensor 3's heater circuit. This triggers the Check Engine Light to be illuminated on the dash. When the heater control circuit malfunctions, it causes readings to not be accurate for bank 1 sensor 3. In rare cases, your 2003 Mercury Grand Marquis may experience rough running and poor fuel economy.

How does a mechanic diagnose the P0043 code?

As with most DTC's, step-by-step diagnostics are required to rule out simple issues before looking at more complex ones. Repair steps are as follows:

• A scan tool is installed into 2003 Mercury Grand Marquis s OBD-II port to check if P0043 is present

• Freeze frame data is observed so conditions for the code being triggered can be recreated

• The code is cleared and a test drive is performed under the same conditions as the freeze frame data indicated.

• If the Check Engine Light returns upon test, then the code is confirmed.

• The technician performs a visual inspection of wiring and bank 1 sensor 3 for any damage, breaks, or shorted wiring.

• Bank 1 sensor 3 voltage is checked to make sure it is not excessively low.

• If low voltage is confirmed, bank 1 sensor 3 is faulty

• If low voltage was not present, a diagnostic of the ECU will be performed, this test is manufacture and 2003 Mercury Grand Marquis -make specific.

Common mistakes when diagnosing the P0043 code

P0043 is an uncommon code. Following all steps and not skipping anything is important so nothing is overlooked. Oxygen sensors should not be cleaned, and if faulty, should be replaced. Always confirm low voltage for oxygen sensor bank 1 sensor 3 before any replacement is performed.

How serious is the P0043 code?

P0043 is generally not a serious code as it usually does not cause any symptoms other than the Check Engine Light. With poor fuel economy and your 2003 Mercury Grand Marquis running roughly, it is recommended to have this code looked at by a qualified technician as soon as possible to ensure safe operation of your 2003 Mercury Grand Marquis .

What repairs can fix the P0043 code?

The most common repairs are as follows:

• Bank 1 sensor 3 replacement
• Repairing or replacing open or short in wiring
• Bank 1 sensor 3 heater circuit fuse replacement
• ECU replacement

Additional comments for consideration regarding the P0043 code

Though this code is more uncommon, it does occur periodically. Following all steps and not jumping to conclusions before checking is important to make fixing this code simple. Refer to manufacture diagrams for the wiring and sensor locations to aid in diagnostics.

Need help with a P0043 code?

Check Engine Light

P0043

trouble codes