If a trouble code P0135 is lighting up the check engine light on our 4.2L V6 equipped Ford E150 or E250, there's a problem with the heating element circuit of the front o2 sensor for bank 1 (O2 B1S1).
In this tutorial, which I've written specifically for the 1997-2000 E150 and E250 with a 4.2L V6 engine, I'll walk you through the meaning of this diagnostic trouble code (DTC) and the most common fixes to get them to go away.
Let's get started!
Contents of this tutorial:
- What Does Trouble Code P0135 Mean?
- What Causes Trouble Codes P0135?
- What Does The O2 Sensor Heater Do?
- How To Resolve Trouble Code P0135.
- Where To Buy The O2 Sensor And Save.
- TEST 1: Making Sure The Heater Element Is Getting 12 Volts.
- TEST 2: Making Sure The Heater Element Is Getting Ground.
- TEST 3: Testing The Heater Element's Resistance.
- More 4.2L Ford E150 And E250 Test Tutorials.
APPLIES TO: This tutorial applies to the following vehicles:
- 4.2L V6 Ford E150: 1997, 1998, 1999, 2000.
- 4.2L V6 Ford E250: 1997, 1998, 1999, 2000.
WIRING DIAGRAM: The following wiring diagram may come in handy:
NOTE: The following tutorial will help you troubleshoot DTC P0141:
What Does Trouble Code P0135 Mean?
Trouble code P0135 indicates a problem with the front oxygen (O2) sensor heater for bank 1 of your van's 4.2L V6 engine. Let's break it down a bit further:
P0135: Heater Circuit Malfunction (Bank 1, Sensor 1)
- Meaning: This code indicates an issue with the heater circuit of the oxygen sensor located upstream from the catalytic converter on the side of the engine where the number 1 cylinder is.
- Bank 1 Sensor 1 (B1S1) Location: This oxygen sensor is located before the catalytic converter that filters exhaust from the bank of cylinders (1, 2, and 3) on the passenger side of the van. Specifically, it's located on the exhaust manifold that's bolted to the right (passenger) side of the engine.
This O2 sensor keeps tabs on the oxygen content of the exhaust gas before it passes through the catalytic converter, giving feedback to the powertrain control module (PCM) about its effectiveness (in adjusting the air/fuel mixture for Bank 1 cylinders). - Other Designations: The B1S1 oxygen sensor, or Bank 1 Sensor 1, goes by different names. Here are the most common ones you'll come across:
- Upstream Right Oxygen Sensor.
- Passenger Side Front Oxygen Sensor.
- Right Front O2 Sensor.
- Bank 1 Pre-Catalytic Converter Oxygen Sensor.
- Possible Causes:
- Faulty oxygen sensor (Bank 1, Sensor 1).
- Damaged wiring or connector to the sensor.
- PCM malfunction (less common).
What Causes Trouble Codes P0135?
The most common causes of trouble code P0135 is the failure of the O2 sensor's heater element. Other issues that can cause the P0135 DTC are wiring problems, such as shorts or open circuits in the sensor's wiring harness.
Here's a more detailed look into the issues that can cause a P0135 DTC:
- Heater Element Failure: The heating element (within the O2 sensor) will eventually burn out due to the extreme temperatures it has to produce and maintain as the engine runs.
- Wiring Problems: The O2 sensor's wires are exposed to heat, vibration, and other environmental factors that can cause them to become frayed, corroded, or damaged, leading to open or short-circuit problems in the heater circuit. The most common cause of a wiring issue is the sensor's wiring touching the hot exhaust pipe or other components, causing a 'short-circuit to Ground' problem.
- PCM malfunction: The PCM is responsible for activating the heater element of the oxygen sensor. While very rare, it's possible for the PCM to malfunction and not be able to activate the oxygen sensor heater.
What Does The O2 Sensor Heater Do?
The 4.2L V6 engine in your Ford E150 (E250) comes equipped with four oxygen sensors. They provide the Powertrain Control Module (PCM) with indispensable feedback regarding the precision of its air-fuel mixture adjustments. There's only one tiny little problem, the O2 sensors are only completely operational once they've reached temperatures in the range of 600 to 800 °F.
So, when you first start up your van's engine, the O2 sensors are not hot enough to activate or are slow to respond to the changes in the air/fuel mixture the PCM is making. This forces the PCM to rely on preset fuel maps and data from other sensors like the mass airflow (MAF) sensor to control the air-fuel mixture needed to keep the engine running optimally.
Once the engine warms up and the O2 sensors reach their operational temperature, they start providing accurate feedback on the oxygen levels in the exhaust. This enables the PCM to fine-tune the air-fuel mixture in real-time, leading to better better gas mileage and emissions control.
Although the oxygen sensors are exposed to the intense heat of the exhaust gas, it isn't enough to consistently get them to reach their optimal temperature. This is especially true during idling or low-load situations when the exhaust gas heat just isn't high enough to maintain the O2 sensors' high operating temperature.
So, to ensure consistent and rapid heating regardless of engine conditions, the sensors are equipped with internal heaters. These heaters, activated by the PCM during engine start-up, swiftly heat up the sensors.
Eventually, the heating elements in the oxygen sensors degrade due to the extreme temperatures they're creating and are exposed to, leading to issues like the P0135 DTC you're currently researching.
How To Resolve Trouble Code P0135
The number 1 solution to DTC P0135 is replacing the oxygen sensor that monitors the exhaust gas as they exit the Bank 1 exhaust manifold. Here are the three main reasons why:
- Simplicity: Swapping out the O2 sensor is a pretty straightforward task. You don't need any advanced/expensive diagnostic equipment or specialized skills, just an O2 sensor socket/wrench tool. For most folks, it's the quickest fix and doesn't require a whole lot of effort.
- Cost-Effectiveness: Compared to other components of the engine management system, O2 sensors are pretty inexpensive, typically ranging from $30 to $50. This affordability makes replacing it the go-to solution for a lot of folks.
- Diagnostic Challenge: Troubleshooting the heater circuit does take time and in some cases, requires a professional-grade scan tool (the ones that run $3,000 or more), along with access to professional diagnostic information. For most folks (even some repair shops), it's more practical to start by replacing the sensor first. The thinking here is that it's really not that common for other underlying issues to be present, such as electrical wiring problems in the O2 sensor heater circuit.
If you want to skip testing the O2 sensor's heating element and just replace the sensor from the get-go, I want to recommend that you:
- Inspect Wiring Harness: Visually inspect the oxygen sensor wiring harness wires. Look for any signs of damage, such as melted insulation or wires that are shorted together.
Damaged wiring can cause the engine not to start. This is because the fuse that supplies power to the O2 sensor's heating element also powers the fuel pump, fuel injectors, and ignition coil. A short circuit in the O2 sensor wiring could blow this fuse.
If you find any issues with the wiring, address them before installing a new oxygen sensor.
To see my oxygen sensor recommendations and where to buy them, go here: Where To Buy The O2 Sensor And Save.
Where To Buy The O2 Sensor And Save
NOTE: Not sure if the oxygen sensors listed above fit your particular vehicle? Don't worry, once you get to the site they'll make sure it fits by asking you the specifics of your particular vehicle. If it doesn't fit, they'll find you the right one.
TEST 1: Making Sure The Heater Element Is Getting 12 Volts
The first thing that we'll do is make sure the that O2 sensor's heating element is getting 10 to 12 Volts when the key is turned to the RUN position.
The wire that delivers this voltage to the O2 sensor's heater element is the red (RED) wire of the 4-wire engine wiring harness connector.
NOTE: Before beginning any of the O2 sensor heater element tests, make sure the engine is cold. If the engine has been running for any length of time, let it cool down completely.
These are the test steps:
- 1
Disconnect the O2 sensor from its engine wiring harness connector.
- 2
Place your multimeter in Volts DC.
- 3
Connect the black multimeter test lead to the battery negative (-) post.
- 4
Turn the key to the RUN position but don't crank or start the engine.
- 5
With the red multimeter test lead, probe the male terminal of the connector that connects to the RED wire of the O2 sensor's 4-wire connector.
- 6
Your multimeter should register 10 to 12 Volts DC.
Let's interpret your test result:
CASE 1: The RED wire is delivering 10 to 12 Volts. This is the correct and expected test result.
Your next step is check that the heater element is getting Ground. Go to: TEST 2: Making Sure The Heater Element Is Getting Ground.
CASE 2: The RED wire IS NOT delivering 10 to 12 Volts. Without this voltage, the heater element will not function.
If the engine in your van starts, the most likely cause of this missing voltage is an open-circuit problem in the RED/WHT between the engine wiring harness O2 sensor connector and the PCM Power Relay.