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Severity: Low Code type: Manufacturer-specific (Ford)

Ford P1152 Code: Lack of Upstream O2 Sensor Switch – Rich (Bank 2)

On a Ford V6 or V8, the bank 2 front O2 sensor sticks on rich even after the PCM leaned that bank out fully.

At a glance

Severity: 2/5 – Low2/5

Severity: Low

Meaning
Lack of Upstream O2 Sensor Switch – Rich (Bank 2)
System
Fuel & Air Metering · Powertrain
Safe to drive?
Yes, short term
Typical repair cost
$0–$2,800
DIY difficulty
Moderate

P1152 is set on two-bank Ford engines when the bank 2 upstream sensor (HO2S-21) holds above roughly 0.45 V while bank 2 fuel trim has already reached its lean limit. Because each bank has its own injectors, sensor and fuel trim, a rich reading on only one side narrows the search a lot: a leaking injector on that bank, coolant or oil fouling that bank's sensor, or a wiring fault in the HO2S-21 circuit. A telling pattern is P1152 stored together with P1131; that combination very often means the bank 1 and bank 2 sensor plugs were crossed during earlier work, so the PCM is correcting the wrong side. If P1132 is present as well, both banks read rich and the cause is common to the whole engine, such as a stuck-open purge valve or high fuel pressure. The code shows up on Ford's modular V8s, the 4.0 V6 and the Duratec 3.0 V6.

Can I keep driving? You can drive it for now, but a truly rich bank overheats that side's catalytic converter over time. If you notice a sweet coolant smell, white exhaust smoke or a falling coolant level, stop and check the cooling system before driving further.

How to read P1152

How to read P1152P11213524
  1. P Powertrain
  2. 1 Manufacturer-specific
  3. 1 Fuel & air metering
  4. 52 Specific fault

Symptoms

  • Check engine light with P1152, sometimes P0175
  • Fuel smell from the exhaust, stronger on one tailpipe on dual-exhaust models
  • Worse fuel economy
  • Bank 2 fuel trims strongly negative compared to bank 1
  • Coolant level dropping without a visible leak (if coolant is fouling the sensor)

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Leaking or stuck-open fuel injector on a bank 2 cylinder 26%
  2. HO2S-21 fouled by coolant from a head gasket or intake leak on that bank 20%
  3. HO2S-21 signal wire shorted to heater power or damaged harness 16%
  4. Bank 1 and bank 2 sensor connectors crossed after previous repairs 14%
  5. Oil burning in bank 2 cylinders (valve stem seals, rings) coating the sensor 12%
  6. Engine-wide rich condition (purge valve, fuel pressure) that shows on bank 2 first 12%

Diagnosis step by step

Diagnostic flow: P11521Look at the full code list2Remove and read the bank 2 sensor3Check the sensor circuit4Inspect bank 2 spark plugs5Test for coolant loss

  1. Look at the full code list

    Note every stored code. P1152 plus P1131 points to crossed sensor plugs; P1152 plus P1132 means both banks are rich and you should start with the purge valve and fuel pressure; P1152 alone keeps the search on bank 2.

    Tools: OBD-II scanner

  2. Remove and read the bank 2 sensor

    Pull HO2S-21 and examine the tip. White or greenish crust suggests coolant or silicone, a wet oily coating suggests oil burning, and dry black soot suggests a genuinely rich bank. Compare against the bank 1 sensor.

    Tools: O2 sensor socket, Flashlight

  3. Check the sensor circuit

    With the sensor unplugged and the key on, the signal wire on the PCM side should read near zero. Battery voltage there means the signal is shorted to the heater feed somewhere in the harness, often where it runs close to the exhaust.

    Tools: Multimeter

  4. Inspect bank 2 spark plugs

    Pull the plugs on bank 2 and compare them. One plug that is wet, black or smelling of fuel identifies the leaking injector; a clean, steam-washed plug points to coolant entering that cylinder.

    Tools: Spark plug socket

  5. Test for coolant loss

    Pressure-test the cooling system and watch the coolant level over several drives. Unexplained loss together with a fouled bank 2 sensor calls for a head gasket or intake gasket check on that side.

    Tools: Flashlight

Where the parts are

Exhaust: catalytic converter and O2 sensors (Bank 1 / Bank 2) – P11521212345
Exhaust: catalytic converter and O2 sensors (Bank 1 / Bank 2)
  1. 1Upstream O2 sensor
  2. 2Catalytic converter
  3. 3Downstream O2 sensor
  4. 4Diesel particulate filter
  5. 5Turbocharger

Repair options & costs

RepairDIY?Estimated cost
Replace bank 2 upstream O2 sensor Yes $150–$380
Correct swapped sensor connectors Yes $0–$80
Replace leaking injector(s) on bank 2 No $250–$850
Repair HO2S-21 harness Yes $80–$250
Replace intake or head gasket (coolant leak) No $700–$2,800

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Emissions / smog test impact

Will fail

With P1152 set, the check engine light is on and an OBD emissions test fails. A rich bank can also raise tailpipe CO where a state still runs a sniffer test on older vehicles.

Frequently asked questions

What does P1131 together with P1152 mean?

Lean on bank 1 and rich on bank 2 at the same time is the classic sign of crossed O2 sensor connectors. The PCM adds fuel to the side that isn't actually lean and removes it from the other, so both trims hit their limits.

Can a head gasket leak cause P1152?

It can. Coolant burned in bank 2 cylinders coats that side's O2 sensor and pushes its reading high. Unexplained coolant loss or white exhaust smoke alongside P1152 is worth taking seriously.

Will a new O2 sensor fix it?

Only if the old one is contaminated or failed. If an injector on bank 2 is leaking, a new sensor will correctly report the same rich mixture and the code returns.

Why is only one side rich if the engine has one fuel pump?

The pump and pressure are shared, but each bank has its own injectors and its own sensor. A fault on one of those parts only affects the bank it belongs to.

Sources