P1122
SubaruThrottle Position (TP) Sensor Circuit Intermittent Low Voltage
Medium SeverityThis here code means your throttle position sensor is sending a weak or broken signal to the engine computer every now and then. When that happens, the computer gets confused about how much you're pressing the gas, which can make your Subaru run like a dog and waste fuel.
⚠️ Before You Begin (Safety First)
Always make sure the engine is off and cooled down before you start poking around. And for Pete's sake, disconnect the battery before you touch any electrical stuff to avoid a shock or frying something else. Keep your hands clear of moving parts too, even if it's off, you never know.
Common Symptoms
- The check engine light comes on, then maybe goes off for a bit, then comes back.
- The engine might idle rough, almost like it's hunting for a comfortable spot.
- You'll feel hesitation or a surge when you try to accelerate, like the car can't decide what to do.
- The automatic transmission might shift hard or at odd times.
- Your gas mileage will probably go down the tubes, burning more fuel than it ought to.
Common Causes
- The throttle position sensor itself is just worn out or faulty, sending a flaky signal.
- There's a loose or corroded connection in the wiring harness going to the sensor, causing a bad contact.
- The wiring insulation might be chafed or broken somewhere, letting the wire short out or lose signal intermittently.
- Water or dirt got into the sensor connector, messing with the electrical flow.
- Though less common, a faulty engine computer (ECM) could be misinterpreting the signal, but usually it's the sensor or the wires.
Frequently reported on: 2002-2007 Subaru Impreza WRX, 2003-2008 Subaru Forester, 2000-2004 Subaru Legacy, 2005-2009 Subaru Outback, 2006-2008 Subaru Tribeca
Diagnostic Steps
- First thing, pop the hood and locate that throttle position sensor, usually right on the throttle body.
- Give the wiring harness connector a good inspection; look for any corrosion, bent pins, or signs of wear.
- Wiggle the connector while the engine is running (if it's safe) to see if the symptoms change or if the check engine light flickers. That'll tell you if it's a loose connection.
- If you've got a multimeter, check for proper voltage at the sensor. You should see a smooth increase in voltage as you slowly open the throttle by hand.
- If the sensor voltage is erratic or drops out, go ahead and replace the throttle position sensor. Make sure you get the right one for your Subaru.
- After replacing, clear the code with a scan tool and take it for a drive to see if the problem comes back. Pay attention to how the car drives.
👨🔧 When to Call a Professional
If you've checked all the simple stuff and you're still chasing your tail with this code, or if the car is just plain undrivable, then it's time to let a professional take a look. Sometimes these intermittent gremlins need proper scan tools and folks who've seen it a hundred times.
Commonly Asked Questions
Can I just ignore this P1122 code for a while?
Well, you could try, but it's like trying to drive a horse with a loose rein. Your car won't run right, your gas mileage will suffer, and eventually, it might leave you stranded. Best to get it sorted, son.
Is it hard to replace the throttle position sensor on a Subaru?
Nah, it ain't rocket science, but it ain't always a five-minute job either. It's usually held on with a couple of screws right on the throttle body. The trick is getting the new one calibrated right, which sometimes means just bolting it on, and other times needs a special procedure. Check your service manual.
What if my wiring looks okay but the code keeps coming back?
Then you've either got a sneaky break in the wire somewhere you can't see, or the sensor itself is just plain faulty even if it looks fine on a simple check. Remember, 'intermittent' means it might work fine until it gets a bump or a bit of heat. Don't rule out the sensor too quickly if the wiring appears solid.
Will a new TPS fix my poor fuel economy?
If that faulty TPS is making your engine computer think you're stomping on the gas all the time when you're not, then absolutely. Getting that sensor to tell the truth again will help your engine get the right amount of fuel, and your economy should get back to normal. It's all about that fuel mixture, you see.