P0052 is a rare and generic OBDII trouble code. It indicates that your Mercury Milan’s heated oxygen sensor is sending a signal to the PCM that is higher than its normal operating range.
Terminology:
- HO2S- Heated Oxygen Sensor
- B2S1- Bank 2, Sensor 1
- PCM- Powertrain Control Module (sometimes called ECM)
P0052 Definition: HO2S – Heater Control Circuit High – Bank 2 Sensor 1
There are three parts to the definition of P0052. The first part is the malfunctioning part on your Milan, the second part indicates what is wrong, and the third part tells you where the malfunctioning HO2S is located.
HO2S
The heated oxygen sensor measures the exhaust after it exits the combustion chamber. The PCM uses this data to maintain the proper 14.7:1 air/fuel ratio.
Heater Control Circuit High
The heated element within the oxygen sensor heats the sensor faster than the exhaust can on its own. This reduces emissions by letting the fuel trim enter closed loop operation more quickly.
Your Milan’s PCM has detected that the heater control circuit resistance is outside the operating range set by Mercury. When this happens, P0052 is stored in the onboard memory.
Bank 2 Sensor 1
B2S1 is the location of the oxygen sensor. Bank 2 is the side of your Milan’s engine with the second cylinder. Bank 2 related codes occur on V6 or V8 engines, so you’ll need to determine which side of the engine bank 2 is on.
If you need help, we’ve written a guide to the B2S1 location.
Sensor 1 is the first in line following bank 2. It’ll be on or directly after the exhaust manifold. It’s finding bank 2 that is the tricky part here.
P0052 Symptoms: Mercury Milan
There usually aren’t any noticeable symptoms for P0052. Once the exhaust heats up, the O2 sensor should still be able to pull a good reading.
Mercury Milan P0052: Causes + Diagnosis
Here are the most common causes of P0052 in the Mercury Milan, as well as a decent order to check them in.
1. Check the Wiring on Bank 2 Sensor 1
CHECK THE WIRING HARNESS FOR DAMAGE since P0052 indicates a fault in the heated O2 sensor circuit.
Pay extra close attention to where the harness may have rubbed up against something or has been damaged by road debris. Look for burnt, frail, or damaged wiring. Wiring issues are a VERY COMMON cause for P0052.
Take a look at where your Mercury Milan’s oxygen sensor plugs into the wiring harness and see if there has been any damage to the pins or if the wiring harness is breaking at the pigtail.
If the pins appear corroded, get some electrical contact cleaner and clean them up. If they are damaged, you will need to repin or replace your wiring harness.
2a. Verify the O2 Sensor is Bad- Swap Test
This method does not work if Mercury Milan has P0032 AND P0052.
Since your Milan happens to be a V6 or V8 model, you can do the “swap test.” This test involves clearing the codes and seeing if the code “jumps” to bank 2. It’s a great test because it’s foolproof and easy to do.
Here’s how the swap test is done:
- Clear the DTC codes with your scanner.
- Swap the Bank 2 Sensor 1 O2 sensor with the Bank 1 Sensor 1. It’ll be on or right after the exhaust manifold.
- Run your Milan’s engine until the check engine light comes back on.
- If the code changes to P0032 (The Bank 1 version of this code), that’s proof enough you need to replace the oxygen sensor you swapped.
- If the code remains P0052, you’ll need to continue pursuing your diagnosis, knowing that both O2 sensors are working fine.
2b. Check the O2 Sensor Heater Resistance
You can test the heater element resistance. This will for sure verify whether the heated element is bad or not.
If there is voltage at the heater circuit, you’ll need to test the ground for resistance. If you find infinite resistance, you’ll need to repair the ground circuit.
This video is short and does a great job of explaining how to test for this.
3. Bad Oxygen Sensor
If the oxygen sensor wiring checked out or failed the swap test, it’s time to replace the heated oxygen sensor. Oxygen sensors go bad all the time. It’s very unlikely that P0052 is caused by a PCM issue.
Conclusion
P0052 is almost always caused by a bad wiring harness or heated oxygen sensor. Good luck repairing your Mercury Milan! Feel free to drop a comment if you can help the next person reading this.