P0122 – Throttle Position Sensor Circuit Low

The P0122 diagnostic trouble code (DTC) indicates that the engine control module (ECM) has detected a low voltage input from the throttle position sensor (TPS) circuit "A". This code is a generic powertrain code that applies to most makes and models.

Urgency and Severity

When the P0122 code triggers, it's generally safe to continue driving the vehicle in the short-term. However, you may experience reduced engine performance, rough idling, or stalling. It's best to diagnose and repair the issue as soon as possible to avoid potential damage to the engine or catalytic converter. If drivability is severely impacted, have the vehicle towed to a repair shop.

Parts Involved

The main component implicated with a P0122 code is the throttle position sensor (TPS). The TPS is located on the throttle body and measures the throttle valve angle and rate of change, sending this information to the ECM. The ECM uses TPS data to regulate air-fuel mixture, ignition timing, and other engine parameters.

Other parts that may be involved include:

• Throttle body
• Wiring and connectors
• ECM (rare)

Common Causes

Potential causes of a P0122 code include:

• Faulty TPS
• Damaged wiring or poor connections in the TPS circuit
• Throttle body issues
• Rarely, a problem with the ECM

Diagnosis Steps

1. Scan for other codes. If multiple codes are present, diagnose them in the order they occurred.

2. Visually inspect the wiring and connectors between the TPS and ECM. Repair any damage.

3. Test the TPS circuit for continuity, proper voltage, and resistance according to manufacturer specifications.

   • Typical TPS reference voltage: 5 V
   • Typical TPS resistance range: 1-10 kΩ

4. If the wiring checks out, replace the TPS.

5. Clear the code and test drive to verify the repair.

Repair Cost

Expect to pay the following for diagnosis and repair of a P0122 code:

• Diagnosis: 1 hour of labor ($75-150 USD, €70-140 EUR)
• TPS replacement: $50-200 USD (€45-180 EUR) for the part plus 1 hour of labor
• Wiring repair: 1-3 hours of labor, plus minimal cost for wiring/connectors

Prevention

To prevent TPS issues:

• Avoid aftermarket "performance chips" that can damage sensors
• Only use high-quality replacement parts
• Address trouble codes promptly
• Maintain the engine properly to minimize carbon buildup on the throttle body

Related Codes

Other codes commonly seen with P0122 include:

• P0121 – Throttle Position Sensor Range/Performance
• P0123 – Throttle Position Sensor "A" High Input
• P0221 – Throttle Position Sensor "B" Range/Performance
• P2135 – Throttle Position Sensor Correlation

Key Specifications

• TPS reference voltage: 5 V
• TPS resistance range: 1-10 kΩ (1,000-10,000 Ω)
• Throttle body bore diameter (varies by engine):
  • 4-cylinder: 45-60 mm (1.75-2.25 in)
  • V6: 60-75 mm (2.25-3.00 in)
  • V8: 75-90 mm (3.00-3.50 in)

Frequently Asked Questions (FAQ) about P0122 Code

What does the P0122 code mean?

The P0122 code indicates that the engine control module (ECM) has detected a low voltage input from the throttle position sensor (TPS) circuit “A”. This means the TPS signal is below the expected range.

Is it safe to drive with a P0122 code?

While it’s generally safe to drive with a P0122 code in the short term, you may experience reduced engine performance, rough idling, or stalling. It’s best to diagnose and repair the issue as soon as possible to avoid potential damage to the engine or catalytic converter.

What are the common symptoms of a P0122 code?

Common symptoms include:

• Illuminated check engine light
• Poor acceleration
• Delayed throttle response
• Rough idle or stalling
• Reduced fuel efficiency

What are the possible causes of a P0122 code?

Potential causes include:

• Faulty throttle position sensor
• Damaged wiring or poor electrical connections in the TPS circuit
• Throttle body issues
• Rarely, a problem with the ECM

How do you diagnose a P0122 code?

Diagnosis steps:

1. Scan for other codes and diagnose them first if present.
2. Visually inspect the wiring and connectors between the TPS and ECM.
3. Test the TPS circuit for continuity, proper voltage, and resistance.
4. If the wiring is okay, replace the TPS.
5. Clear the code and test drive to verify the repair.

Can a P0122 code cause transmission problems?

Yes, since the TPS helps control transmission shift points and pressures, a faulty TPS can lead to poor shift quality and other transmission issues.

What is the typical repair cost for a P0122 code?

Expect to pay:

• $75-$150 for diagnosis
• $50-$200 for a new TPS plus 1 hour of labor
• 1-3 hours of labor plus minimal cost for wiring repairs

How can I prevent TPS issues?

To prevent TPS problems:

• Avoid aftermarket “performance chips”
• Only use high-quality replacement sensors
• Address trouble codes promptly
• Maintain the engine to minimize carbon buildup on the throttle body

What other codes may appear with P0122?

Related codes include:

• P0121 – TPS Range/Performance
• P0123 – TPS “A” High Input
• P0221 – TPS “B” Range/Performance
• P2135 – TPS Correlation

What tools are needed to diagnose a P0122 code?

To properly diagnose a P0122 code, you’ll need:

• An OBD-II scanner
• A digital multimeter
• Basic hand tools

Can a bad TPS cause a car to not start?

In rare cases, a severely faulty TPS can prevent the engine from starting if it sends an incorrect signal to the ECM. However, hard starting is more commonly associated with a P0123 (high input) code.

Is the throttle position sensor the same as the accelerator pedal position sensor?

No, while they work together, the TPS measures the actual throttle valve angle, while the accelerator pedal position sensor measures pedal movement. Some vehicles use a combined sensor.

What does TPS voltage refer to?

TPS voltage is the signal voltage the sensor sends to the ECM indicating throttle position. A typical TPS has a 5V reference voltage and outputs 0.5-4.5V depending on throttle angle.

Can you replace just the TPS or do you have to replace the whole throttle body?

On most vehicles, the TPS itself is replaceable. However, some newer drive-by-wire designs integrate the TPS into the throttle body, requiring replacement of the entire unit.

How do you perform a TPS adjustment?

TPS adjustment involves physically rotating the sensor to align it with the throttle valve. This is typically only necessary on older vehicles with adjustable TPS designs and cable-operated throttles.

What is the difference between TPS “A” and “B” circuits?

Many vehicles use two TPS circuits (A and B) for redundancy and diagnostics. The A circuit is the primary signal, while B is a crosscheck. A and B voltages should mirror each other; if not, a correlation code like P2135 may set.

Can a P0122 code cause a vehicle to fail an emissions test?

Yes, a faulty TPS can lead to an emissions test failure by causing incorrect air-fuel mixture and inefficient combustion. The code must be repaired and the readiness monitors reset before retesting.

What does “low input” mean in the P0122 code description?

“Low input” indicates that the voltage signal from the TPS sensor is below the expected range, typically less than 0.2-0.3V at closed throttle. This points to an “open” in the TPS wiring or a faulty sensor.

Can a weak battery cause a P0122 code?

Rarely, a weak battery or charging system can cause low voltage to the TPS and trigger a P0122. However, this is unlikely as the code specifically indicates a problem with the TPS circuit.

How do you test a throttle position sensor?

To test a TPS:

1. Unplug the sensor and test the reference voltage (should be 5V).
2. Check continuity between the ground wire and ECM.
3. Measure the sensor resistance (typically 1-10 kΩ).
4. Reconnect the sensor and backprobe the signal wire with a multimeter. The voltage should smoothly increase as you open the throttle.