Ford F-150 Bank 1 Sensor 1 Location: Passenger-Side Upstream O2 Sensor
Quick answer: On Ford F-150 V6 and V8 engines, Bank 1 is the passenger (right) side, the side with cylinder 1. Bank 1 Sensor 1 (Ford calls it HO2S11) is the upstream oxygen sensor on the passenger side, before the catalytic converter. It threads into the front exhaust pipe just below the exhaust manifold (below the turbocharger on the 3.5L EcoBoost), and you reach it from under the truck. The sensor after the converter on the same side is Bank 1 Sensor 2.
Where Is Bank 1 Sensor 1 on a Ford F-150?
“Bank” is the row of cylinders, and “sensor” is the position along the exhaust, counted from the engine. Ford’s cylinder identification diagrams for the 2008 F-150 5.4L, the 2011 5.0L and the 2011 3.5L EcoBoost all put cylinder 1 at the front of the right-hand (passenger) bank. That makes the passenger side Bank 1 and the driver side Bank 2.
Ford’s catalyst and exhaust system description says only two oxygen sensors are used in each exhaust stream. The front sensors (HO2S11/HO2S21) before the catalyst handle fuel control. The sensors after the catalyst (HO2S12/HO2S22) monitor catalyst efficiency. A V6 or V8 F-150 with one exhaust stream per bank therefore has four oxygen sensors:
| Scan tool name | Ford name | Side of truck | Position | What it does |
|---|---|---|---|---|
| Bank 1 Sensor 1 (B1S1) | HO2S11 | Passenger (right) | Upstream, before the catalytic converter | Fuel control for cylinders on Bank 1 |
| Bank 1 Sensor 2 (B1S2) | HO2S12 (catalyst monitor sensor) | Passenger (right) | Downstream, after the catalytic converter | Monitors Bank 1 catalyst efficiency |
| Bank 2 Sensor 1 (B2S1) | HO2S21 | Driver (left) | Upstream, before the catalytic converter | Fuel control for cylinders on Bank 2 |
| Bank 2 Sensor 2 (B2S2) | HO2S22 (catalyst monitor sensor) | Driver (left) | Downstream, after the catalytic converter | Monitors Bank 2 catalyst efficiency |
“Left” and “right” are as seen from the driver’s seat. If you’re lying under the truck facing up and looking forward, Bank 1 is on your right. For a full four-sensor walkthrough, see our F-150 oxygen sensor location guide, how many O2 sensors an F-150 has and where the O2 sensors are on an F-150.
Bank 1 Sensor 1 by F-150 Engine
| Engine | Bank 1 cylinders (passenger side) | Upstream sensor type (Ford) | Ford HO2S torque |
|---|---|---|---|
| 5.4L V8 (2008 F-150) | 1, 2, 3, 4 (Ford) | Heated oxygen sensor (HO2S) #11 | 46 Nm (34 lb-ft) (Ford) |
| 3.5L EcoBoost V6 (2011 F-150) | 1, 2, 3 (Ford) | Universal (wide-band) HO2S #11, after the turbo | 48 Nm (35 lb-ft) (Ford) |
| 5.0L V8 (2011 F-150) | 1, 2, 3, 4 (Ford) | Universal (wide-band) HO2S #11 | 48 Nm (35 lb-ft) (Ford) |
| 6.2L V8 (2011 F-150) | Check your Ford cylinder ID diagram | Universal (wide-band) HO2S #11 | 46 Nm (34 lb-ft) (Ford) |
| Inline engines (e.g. older 4.9L six) | All cylinders (one bank only) | Bank 1 sensors only, no Bank 2 | See your Workshop Manual |
On 2015 and later F-150 engines (2.7L and 3.5L EcoBoost, 3.3L V6, 5.0L), scan tools use the same Bank/Sensor names. Confirm the bank against the cylinder identification diagram in your Workshop Manual before buying a sensor. On the 3.5L EcoBoost, Ford’s exploded view shows each upstream sensor in the front pipe at the turbo outlet, with the catalyst monitor sensor threaded into the catalytic converter body below it. Cylinder numbering for the 3.5L is explained in our Ford 3.5 V6 cylinder numbering guide.
Is Bank 1 Sensor 1 Upstream or Downstream?
Upstream. “Sensor 1” is always the one closest to the engine, ahead of the catalytic converter. “Sensor 2” is downstream, after the converter. Ford’s HO2S monitor description calls the upstream sensor the “fuel control” or “stream 1” sensor. The PCM checks its output voltage and how fast it switches. The rear sensor is checked for output voltage and used for catalyst monitoring.
Bank 1 vs Bank 2: Which Side Is Which?
| Bank 1 | Bank 2 | |
|---|---|---|
| Side of an F-150 | Passenger (right) | Driver (left) |
| V8 cylinders (5.4L, 5.0L) | 1–4 | 5–8 |
| V6 cylinders (3.5L EcoBoost) | 1–3 | 4–6 |
| Upstream sensor | B1S1 / HO2S11 | B2S1 / HO2S21 |
| Downstream sensor | B1S2 / HO2S12 | B2S2 / HO2S22 |
If your code is for the driver side instead, see our F-150 Bank 2 Sensor 1 location page and the Bank 2 Sensor 1 replacement guide.
Codes That Point to Bank 1 Sensor 1
These are the standard OBD-II code definitions (SAE J2012). A sensor code does not always mean a bad sensor. Wiring, connector, heater fuse and exhaust leak problems can set the same codes.
| Code | Meaning | What to check first |
|---|---|---|
| P0130 | O2 sensor circuit, Bank 1 Sensor 1 | Connector and wiring to the passenger-side upstream sensor |
| P0131 / P0132 | B1S1 circuit low / high voltage | Shorts in the harness, a damaged sensor |
| P0133 | B1S1 slow response | Aged or contaminated sensor, exhaust leak ahead of the sensor |
| P0134 | B1S1 no activity detected | Open circuit, unplugged connector, dead sensor |
| P0135 | B1S1 heater circuit | Heater power and ground circuit, sensor heater |
| P2195 / P2196 | B1S1 signal stuck lean / stuck rich | Air leaks, fuel pressure, MAF, then the sensor |
| P0171 / P0172 | System too lean / too rich, Bank 1 | Whole-bank fuel trim problem, not one cylinder (see below) |
| P0136–P0141 | Bank 1 Sensor 2 (after the cat) | Same side, downstream sensor |
What does “lean Bank 1” (P0171) mean?
It doesn’t mean cylinder 1 is lean. Ford’s fuel system monitor sets P0171 (Bank 1) or P0174 (Bank 2) when the adaptive fuel trim for that whole bank has reached its limit while trying to correct a lean condition. P0172 and P0175 are the rich versions. If both P0171 and P0174 are set, look for something common to both banks, such as an intake air leak after the MAF sensor or low fuel pressure. If only Bank 1 is lean, look for a leak or problem on the passenger side, including an exhaust leak ahead of the B1S1 sensor.
How the Bank 1 Sensor 1 Works
F-150s have used two upstream sensor designs, and they read differently on a scan tool:
| Conventional heated O2 sensor (HO2S) | Universal / wide-band HO2S | |
|---|---|---|
| Used as B1S1 on | 2008 F-150 5.4L, and as the downstream sensor (#12/#22) on 2011 trucks | 2011 F-150 3.5L EcoBoost, 5.0L and 6.2L (upstream) |
| Signal | 0–1.1 V; below 0.4 V = lean, above 0.6 V = rich (Ford) | The PCM measures pump current and reports air/fuel ratio, not a switching voltage (Ford) |
| Heater temperature | About 800°C (1,472°F) | 780–830°C (1,436–1,526°F) |
| On a scan tool | A voltage that switches between lean and rich in closed loop (Ford monitors the switch time) | An air/fuel ratio or lambda value, not a switching voltage |
Ford says the engine enters closed-loop fuel control once the sensor reaches about 300°C (572°F). The heater gets it there sooner after a cold start. The check engine light comes on after the HO2S monitor finds the same concern on two consecutive drive cycles (Ford). For other warning-light causes, see our Ford check engine light guide.
How to Replace Bank 1 Sensor 1 on an F-150
This follows Ford’s HO2S removal and installation procedure (2008 F-150) and the notes in Ford’s 2011 oxygen sensor exploded view:
- Let the exhaust cool fully. Raise the truck safely (Ford’s procedure puts it in NEUTRAL on a hoist).
- Find the passenger-side upstream sensor ahead of the catalytic converter and follow its wire to the connector. Unplug the connector and release the harness retainer.
- If the sensor is seized, apply penetrating and lock lubricant (Ford XL-1).
- Remove the sensor with an oxygen sensor socket. Ford’s tool is 303-476 (T94P-9472-A).
- Apply high-temperature nickel anti-seize (Ford XL-2) to the threads of the new sensor if they aren’t already coated.
- Install and tighten to Ford’s spec: 46 Nm (34 lb-ft) on the 2008 F-150, 48 Nm (35 lb-ft) on the 2011 3.5L EcoBoost, 3.7L and 5.0L, or 46 Nm (34 lb-ft) on the 2011 6.2L. Ford notes that the correct torque wrench setting must be calculated when you use the oxygen sensor socket.
- Reconnect the wiring, clear the codes and drive the truck so the HO2S monitor can run again.
Match the replacement to the position: a Bank 1 Sensor 1 on a 5.0L or EcoBoost is a wide-band unit and is not interchangeable with the downstream sensor. Check the part against your VIN.
Frequently Asked Questions
Is Bank 1 on the driver or passenger side of a Ford F-150?
The passenger (right) side. Bank 1 is the bank that contains cylinder 1, and Ford’s cylinder identification diagrams for the F-150 5.4L, 5.0L and 3.5L EcoBoost put cylinder 1 at the front of the passenger-side bank.
Is Bank 1 Sensor 1 upstream or downstream?
Upstream. Sensor 1 is ahead of the catalytic converter and is used for fuel control. Sensor 2 is after the converter and monitors catalyst efficiency.
Where is Bank 1 Sensor 1 on a 3.5 EcoBoost F-150?
It is in the passenger-side front exhaust pipe at the turbocharger outlet, ahead of the catalytic converter. On the 2011 3.5L EcoBoost, Ford calls it the universal heated oxygen sensor #11, a wide-band sensor.
How many oxygen sensors does a Ford F-150 have?
A V6 or V8 F-150 has four: one upstream and one downstream sensor on each bank (HO2S11, HO2S12, HO2S21 and HO2S22). Ford says only two oxygen sensors are used in each exhaust stream.
Does P0171 lean Bank 1 mean cylinder 1 is lean?
No. Ford’s fuel system monitor sets P0171 when the fuel trim for the whole Bank 1 side reaches its limit correcting a lean condition. Common causes are air leaks, fuel delivery or MAF problems, not only the oxygen sensor.
What is the torque for an F-150 Bank 1 Sensor 1?
Ford lists 46 Nm (34 lb-ft) for the 2008 F-150, 48 Nm (35 lb-ft) for the 2011 3.5L EcoBoost, 3.7L and 5.0L, and 46 Nm (34 lb-ft) for the 2011 6.2L. Apply anti-seize to the threads.
Where is Bank 2 Sensor 1 on an F-150?
On the driver (left) side, upstream of the driver-side catalytic converter. It is the mirror image of Bank 1 Sensor 1.
Sources: Ford service information for the 2008 F-150 5.4L and the 2011 F-150 3.5L EcoBoost and 5.0L (via Operation CHARM): engine cylinder identification, catalyst and exhaust systems, HO2S and universal HO2S descriptions, fuel system monitor, HO2S monitor, 2011 torque specifications and 2008 HO2S removal and installation. Code definitions are the standard SAE J2012 OBD-II meanings.
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