P0038 is a somewhat rare and OBDII trouble code with the Mercury Montego. It means that the heated oxygen sensors (which we’ll be referring to as HO2S a lot) heater control circuit located at B1S2 is sending a signal to the PCM that is outside of its normal operating range. In this case, the signal is higher than it should be.
P0038 should not be considered a breakdown risk. The HO2S in question is downstream of the catalytic converter and is mainly just for emissions purposes.
The causes of P0038 are almost always a bad HO2S or a wiring issue.
Jargon in this Article:
- HO2S– Heated Oxygen Sensor
- B1S2– Bank 1, Sensor 2
- PCM– Powertrain Control Module (sometimes called ECM)
P0038 Definition: HO2S – Heater Control Circuit High – Bank 1 Sensor 2
There are three parts to the definition of P0038. The first part is the malfunctioning part on your Montego, 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 your Mercury Montego’s 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.
In the case of P0038, your Montego’s PCM has detected that the heater control circuit resistance is outside the manufacturer’s specified range.
Bank 1 Sensor 2
Bank 1 Sensor 2 is the location of the oxygen sensor. Bank 1 is the side of your Montego’s engine with the first cylinder.
You only need to concern yourself with this if you have a V6 or V8 engine. If you have a four-cylinder or inline-six, there is only one bank.
Sensor 2 is the first oxygen sensor “downstream” of the catalytic converter.
P0038 Symptoms: Mercury Montego
There usually aren’t any noticeable symptoms for P0038, whatsoever.
P0038 Mercury Montego: Diagnosis
Here are the most common causes of P0038 in the Mercury Montego, as well as a decent order to check them in.
1. Check the Wiring on Bank 1 Sensor 2
CHECK THE WIRING HARNESS FOR DAMAGE since P0038 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 P0038.
Take a look at where your Montego’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
If your Montego happens to be a V6 or V8 model, you can do the “swap test”, if there is a catalytic converter for each side of the exhaust. If the exhaust feeds into one converter, this won’t work.
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 2 O2 sensor with the Bank 1 Sensor 2. It’ll be right after the catalytic converter
- Run your Montego’s engine until the check engine light comes back on.
- If the code changes to P0058 (The Bank 2 version of this code), that’s proof enough you need to replace the oxygen sensor you swapped.
- If the code remains P0038, 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 YouTube video can help you test it.
3. Bad Oxygen Sensor
If the oxygen sensor wiring checked out or the code jumped with the swap test, it’s time to replace the heated oxygen sensor at B1S2. Oxygen sensors go bad all the time. It’s very unlikely that P0038 is caused by a PCM issue.
Conclusion
P0038 is almost always caused by a bad wiring harness or heated oxygen sensor. Good luck fixing your Mercury Montego!