For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC P1174: Fuel Trim Cylinder Balance

### Circuit/System Description

The Fuel Trim Cylinder Balance diagnostic detects a rich or a lean cylinder-to-cylinder air/fuel ratio imbalance. The diagnostic monitors the pre-catalyst heated oxygen sensor (HO2S) signal's frequency and amplitude characteristics by calculating an accumulated voltage over a predetermined sample period. An imbalance is indicated when multiple samples of the accumulated voltage are consistently higher than the desired value.

### Conditions for Running the DTC

• | DTCs P0030, P0053, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0128, P0131, P0132, P0133, P0134, P0135, P0201-P0204, P0220, P0222, P0223, P0300, P0442, P0443, P0446, P0449, P0451, P0452, P0453, P0454, P0455, P0496, P060D, P1133, P1516, P2101, P2119, P2120, P2122, P2123, P2125, P2127, P2128, P2135, P2138, P2176, P2A00 are not set.

• | The device control is not active.

• | The intrusive diagnostics are not active.

• | The engine overspeed protection is not active.

• | The traction control is not active.

• | The fuel control is in air-fuel Closed Loop.

• | The system voltage is greater than 10 volts, or less than 18 volts.

• | The engine run time is greater than 50 seconds.

• | The engine coolant temperature (ECT) is greater than 10°C (50°F).

• | The engine speed is greater than 1,000 RPM, but less than 4,000 RPM.

• | The mass air flow is greater than 7 g/s, but less than 400 g/s.

• | This DTC runs continuously when the above conditions are met.

### Conditions for Setting the DTC

Multiple samples of the pre-catalyst HO2S accumulated voltage are consistently higher than the desired value.

### Action Taken When the DTC Sets

DTC P1174 is a Type B DTC.

### Conditions for Clearing the MIL/DTC

DTC P1174 is a Type B DTC.

### Diagnostic Aids

• | The Fuel Trim Cylinder Balance diagnostic is very sensitive to HO2S design. A non-OE sensor or an incorrect part number may set a false DTC.

• | Monitoring the misfire current counters, or misfire graph, may help to isolate the cylinder that is causing the condition.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

1. Read and record the Freeze Frame/Failure Records data taking note of the speed and load at which the DTC set.
2. Diagnose any other DTCs that are set. Refer to Diagnostic Trouble Code (DTC) List - Vehicle.
3. With the engine idling and the transmission in the Park or Neutral position, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor parameter should be between 19-42 kPa.

⇒ | If the MAP sensor parameter is not between 19-42 kPa, refer to DTC P0106.

4. Inspect the air induction system for modified, damaged, leaking, or restricted components.
5. Inspect the crankcase ventilation system for improper operation. Refer to Crankcase Ventilation System Inspection/Diagnosis.
6. Inspect the vacuum hoses for splits, kinks, and improper connections.
7. Inspect for vacuum leaks at the intake manifold, the throttle body, and the injector O-rings.
8. Test for a restricted, damaged, leaking, or modified exhaust system from the catalytic converter forward. Refer to Symptoms - Engine Exhaust.
9. Test the fuel injectors for improper operation. Refer to Fuel Injector Diagnosis.
10. Test for fuel contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis.
11. Test for excessive fuel in the crankcase due to leaking injectors.
12. Test the ignition system for improper operation. Refer to Electronic Ignition (EI) System Diagnosis.
13. Test the engine for any mechanical conditions such as sticking valves, lifters, etc., which could alter the flow into the combustion chamber. Refer to Symptoms - Engine Mechanical.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verify the repair under the same speed and load as noted in the Freeze Frame/Failure Records data recorded during testing.

• | Air Cleaner Assembly Replacement

• | Air Cleaner Element Replacement

• | Fuel Injector Replacement

• | Fuel System Cleaning

• | Fuel Tank Draining

• | Ignition Coil Replacement

• | Intake Manifold Replacement

• | Spark Plug Replacement

• | Throttle Body Assembly Replacement