Mechanics

A SCAN TOLD ME I HAVE A BAD THROTTLE SENSOR. COULD IT JUST BE A LOOSE WIRE, AND HOW CAN I FIND IT?

2004 Nissan Maxima

How hard and costly is it to replace a bad throttle sensor? I had a hard impact and was wondering if something just got knocked lose. What other reason could have caused the whole sensor to fail. I was thinking maybe a wire was loose, and need to know where to check first before buying the part.
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Justinstill
March 22, 2012.



The fault didn't say the sensor was bad. It said the voltage was too high or too low. Sensors are only responsible for setting codes about half the time. You're one of the few people who are right to suspect wiring problems first. Measure the voltages on the sensor wires by back-probing through the back of the connector while it's still plugged in, then holler back with those numbers.

Caradiodoc
Mar 22, 2012.
I suspected a wire problem because I had a wreck at a low speed when a tree fell into the road in front of me and I had no time to stop. I felt like it jarred something loose, rather than messing up a sensor. A scan at an Autozone revealed a code 1122, throttle position sensor. Where are the sensor wires located, in front of the flex tube? How do I check the voltage, do I put the positive to the wire and just ground the negative somewhere?

Tiny
Justinstill
Mar 22, 2012.
The engine surges, if that helps you any.

Tiny
Justinstill
Mar 22, 2012.
I can't find a decent picture of the sensor but it appears to be part of a larger black plastic housing on the side of the throttle body assembly. There should be three wires going to it.

Ground the black meter lead to the battery negative post or a paint-free spot on the engine. Poke the red probe through the rubber weather seal on the connector. You can use a stretched-out paper clip too if necessary. What you should find is one wire reads about 0.2 volts, one reads 5.0 volts, and the middle one will read from approximately 0.5 at idle to 4.5 volts at wide-open-throttle.

If that middle signal wire always reads close to 5 volts, the ground wire is open, (broken). If it always reads near 0 volts, the 5.0 volt feed wire is open. The signal wire is a little trickier. If it is open, the voltage swing will be correct at the sensor but at the computer it is designed to be "pulled up" to 5 volts or "pulled down" to 0 volts to force the computer to detect the problem and set a code.

The easiest way to check the sensor's operation is with a scanner that displays live data. You can simply sit in the car and work the gas pedal while watching the TPS voltage. If it swings normally from 0.5 to 4.5 volts, all of the wires and sensor are okay.

I just looked up the exact fault code description: P1122 – Throttle Position (TP) Sensor Inconsistent With MAF Sensor Low Voltage

That doesn't indicate a defective sensor, ... Exactly. It means the two sensors don't agree on some engine operating condition. The MAF sensor reports incoming air by weight which is low during idle. The throttle has to be closed and the TPS reading should be near 0.5 volts. The TPS is a relatively simple mechanical device that for the most part can develop an intermittent connection between its movable contact and the carbon strip it rides on, but the MAF sensor has a bunch of electronic circuitry inside so it is more likely to develop a problem like what the fault code is describing. Either sensor can cause an intermittent problem too. The fault code should always be recorded, as you did, then for intermittent problems, it should be erased after any repairs to see if it comes back. Codes will be set by unplugging any sensor while the ignition switch is in the "run" position too so do any work in checking connector pins with the switch off.

Given the code and the history of events, you might look closer at the tube between the mass air flow sensor and the throttle body. Any gap in that tube that lets fresh air in will cause a problem. The throttle blade will be open allowing more air in, but if any air goes in that doesn't go through the MAF, the computer won't know about it and won't command sufficient fuel to go with that air. Based on the throttle position sensor's voltage reading, the computer expects to see a corresponding air flow reading from the mass air flow sensor. THAT is the discrepancy the fault code is referring to.

Caradiodoc
Mar 22, 2012.
2x2 inch hole in right above air filter in housing, in front of the MAF sensor, would that cause the problem?

Tiny
Justinstill
Mar 22, 2012.
Absolutely, but only if it is after the mass air flow sensor. With a hole that big, it's surprising the engine would get any gas at all and run.

Caradiodoc
Mar 22, 2012.
It is in front of maf sensor. Is that sensor comin to go out? Maybe the peace of plastic got stuck n throttle body how far does that open. Trouble shoten driven me craze.

Tiny
Justinstill
Mar 22, 2012.
Plus I unpluged the bank one o2 sensor the one that is in the exhaust manifold under the heat sheild an it ran perfect?So I thought it was that be for the scan.?

Tiny
Justinstill
Mar 22, 2012.
There can't be any leak between the MAF sensor and the throttle body.

As for the oxygen sensor, it only detects unburned oxygen and if there's too much of that, it's going to instruct the computer to alter fuel metering. By unplugging it, while it will change how the engine runs, it's simply eliminating some of the information the computer uses to base those calculations. Those sensors don't even work at all until they get up to 600 degrees, so if the sensor was the problem, the engine would run fine for the first minute or two.

Caradiodoc
Mar 22, 2012.
That sensor is considered an oxygen sensor but one picture I saw said it was air to fuel ratio sensor, when I unplugged it, it ran good till car warmed up. Then went back to what it was doing before. Would that sensor cause the scan tool to throw the other code? Also, the picture of the tbs in on partsgeek. Com, if you need it.

Tiny
Justinstill
Mar 22, 2012.
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