P1120
HondaP1120 indicates that the Powertrain Control Module (PCM) has detected the throttle position sensor (TPS) output voltage is outside its expected operational range, either too high or too low, for a specific period of time or under certain operating conditions.
Medium SeverityThis code means your car's computer isn't getting a good signal from the throttle position sensor, which tells it how much you're pressing the gas pedal. When this sensor misbehaves, the engine struggles to know how much fuel and air it needs, leading to noticeable driving issues and sometimes leaving you stranded.
⚠️ Before You Begin (Safety First)
Always turn off the engine and disconnect the negative battery terminal before working on electrical components to prevent accidental shorts or injury. Be mindful of hot engine parts and rotating components.
Common Symptoms
- Check Engine Light illuminated
- Poor throttle response
- Hesitation or surging during acceleration
- Rough idle
- Engine stalling, especially when coming to a stop
- Vehicle enters 'limp mode' (reduced power)
Common Causes
- Faulty throttle position sensor (TPS)
- Damaged or corroded wiring or connector to the TPS
- Loose TPS mounting or mechanical damage to the throttle body linkage
- Dirty or sticky throttle body plate restricting movement
- Less commonly, an issue with the Powertrain Control Module (PCM)
Frequently reported on: Honda Civic 2001-2005, Honda Accord 1998-2002, Honda CR-V 1999-2004, Honda Odyssey 1999-2004, Honda S2000 2000-2005
Diagnostic Steps
- First, visually inspect the throttle body area. You're looking for any obvious damage or loose connections on the TPS itself or its wiring harness. Sometimes, it's just a simple physical issue rather than a bad sensor. Check for any debris preventing the throttle plate from fully closing or opening.
- Next, check the TPS connector and wiring. Disconnect the connector and inspect for bent pins, corrosion, or frayed wires. A poor connection is a common culprit. Use an electrical contact cleaner if you see any corrosion.
- Now, to really learn what's happening, you'll want to test the TPS sensor's voltage output. With the ignition on (engine off), backprobe the TPS signal wire. As you slowly open and close the throttle by hand, the voltage should smoothly increase and decrease without any drops or spikes. This tells you if the sensor is providing a consistent signal to the computer.
- If the voltage test shows erratic readings, the next step is often to replace the throttle position sensor. This usually involves removing a few screws and swapping out the old sensor for a new one. Remember, some TPS sensors are integrated into the throttle body and cannot be replaced separately.
- Finally, after replacement, clear the P1120 code using an OBD-II scanner. Then, start the engine and test drive the vehicle to see if the symptoms are gone and the code doesn't return. This confirms your repair was successful.
👨🔧 When to Call a Professional
If you've checked the wiring, cleaned the throttle body, and even replaced the sensor, but the problem persists, it's time to consult a professional technician. They have advanced diagnostic tools to verify the PCM's inputs and outputs, ensuring the issue isn't a deeper computer or wiring harness fault.
Commonly Asked Questions
What exactly does the throttle position sensor do?
The throttle position sensor (TPS) is like the engine's ear for your foot. It tells the car's computer (the PCM) exactly how far the throttle plate is open. This information is crucial for the PCM to calculate the correct fuel injection and ignition timing. Think of it as translating your pedal input into electrical signals for the engine.
Can I drive with a P1120 code?
While you might be able to drive your Honda with a P1120 code, it's not a good idea to put it off. You'll likely experience poor performance, like surging or stalling, which can be unpredictable and unsafe. Plus, an incorrect signal can mess with fuel economy and potentially lead to other engine issues down the road if not addressed.
Is cleaning the throttle body always necessary with a TPS issue?
Not always necessary, but it's a smart diagnostic step. Sometimes, a dirty or carbon-fouled throttle body can cause the throttle plate to stick or not return to its proper idle position, which can mimic a TPS fault or even put stress on the TPS. Cleaning it ensures the mechanical side is sound before you condemn the sensor itself.
How do I know if it's the TPS or just the wiring?
That's a great question, and it's why testing the voltage output of the TPS is so important. If you're getting a consistent 5-volt reference to the sensor, a good ground, but the signal wire's voltage isn't smooth as you move the throttle, then the sensor itself is likely the problem. If you lose power or ground at the sensor, then you need to trace those wires back. Learning to test those circuits helps you pinpoint the exact fault.