AutoCodes – Ford – P1129 Ford

P1129 Ford Code - Downstream Oxygen Sensors Swapped from Bank to Bank

Quick Answer

The heated oxygen sensor (HO2S) monitor determines if the HO2S signal response for a fuel shift corresponds to the correct engine bank. Common causes include Crossed HO2S harness connectors (downstream), Crossed HO2S wiring at the harness connectors (downstream), Crossed HO2S wiring at the 104-pin harness connectors (downstream). Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P1129 Ford indicates Downstream Oxygen Sensors Swapped from Bank to Bank .
Common causes: Common causes include Crossed HO2S harness connectors (downstream), Crossed HO2S wiring at the harness connectors (downstream), Crossed HO2S wiring at the 104-pin harness connectors (downstream).
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 11,768

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Apr 27, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P1129 Ford Description

The heated oxygen sensor (HO2S) monitor determines if the HO2S signal response for a fuel shift corresponds to the correct engine bank. The test fails when a response from the HO2S being tested is not indicated.

OBDII Code P1129 Ford - Downstream Oxygen Sensors Swapped from Bank to Bank - AutoCodes.com — P1129 Ford Code - Downstream Oxygen Sensors Swapped from Bank to Bank

What does this mean?

What are the Possible Causes of the DTC P1129 Ford?

Crossed HO2S harness connectors (downstream) Crossed HO2S wiring at the harness connectors (downstream) Crossed HO2S wiring at the 104-pin harness connectors (downstream)

How to Fix the DTC P1129 Ford?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P1129 Ford code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P1129 Ford code?

Need more information on how to fix the P1129 Ford code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P1129 Ford code diagnosed by a professional: Find a repair shop in your area

Information for Specific Ford Models

P1129 1997 Ford F150 — Downstream Oxygen Sensors Swapped from Bank to Bank
P1129 1998 Ford F150 — Downstream Oxygen Sensors Swapped from Bank to Bank
P1129 1999 Ford F150 — Downstream Oxygen Sensors Swapped from Bank to Bank
P1129 2000 Ford F150 — Downstream Oxygen Sensors Swapped from Bank to Bank
P1129 2001 Ford F150 — Downstream Oxygen Sensors Swapped from Bank to Bank
P1129 2002 Ford F150 — Downstream Oxygen Sensors Swapped from Bank to Bank
P1129 2003 Ford F150 — Downstream Oxygen Sensors Swapped from Bank to Bank

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P1129 Ford Code

1. What does the OBDII code P1129 mean for a Ford vehicle?

P1129 indicates that the downstream oxygen sensors have been swapped or installed incorrectly between Bank 1 and Bank 2.

2. What are the symptoms of the P1129 code on a Ford?

Symptoms may include poor fuel economy, rough idling, reduced engine performance, and the illumination of the check engine light.

3. What causes the P1129 code to appear on a Ford?

The code is typically caused by the downstream oxygen sensors being installed in the wrong banks or a wiring issue that has crossed the sensor connections.

4. Can driving with the P1129 code damage my Ford vehicle?

While it may not cause immediate damage, driving with incorrect sensor placement can lead to improper air-fuel mixture adjustments, potentially harming the engine over time.

5. How can I fix the P1129 code on my Ford?

Fixing the code involves verifying the installation of the downstream oxygen sensors and ensuring they are correctly connected to their respective banks.

6. How can I tell which oxygen sensor is on Bank 1 or Bank 2?

Bank 1 refers to the side of the engine with cylinder 1, while Bank 2 is on the opposite side. Refer to your vehicle’s service manual for exact sensor locations.

7. Can a faulty oxygen sensor cause the P1129 code?

A faulty sensor is less likely to cause this code; it is more commonly related to swapped sensor placement or wiring errors.

8. Will clearing the P1129 code fix the issue permanently?

Clearing the code will reset the check engine light temporarily, but the issue will return unless the sensors are correctly installed and connected.

9. How much does it cost to repair the P1129 code on a Ford?

Costs can vary depending on labor rates and whether new sensors or wiring repairs are needed, but it may range from $50 to $300.

10. Can a DIYer fix the P1129 code on a Ford?

Yes, a DIYer can fix this code by carefully checking the sensor placements and connections, provided they have basic tools and access to the vehicle’s repair manual.