Press oil pedal, no acceleration.Transmission does not shift

[smart2003]

My car is 2008 nissan altima 2.5s CVT. Now there are 57,000 mils on it. Several days ago, the tire pressure light turned on (The tire pressure is normal, so dealer said the tire pressure sensor need to be replaced). Yesterday, the "Engine service soon" light is on. When I pressed the oil peday, no normal acceleration. The speed is only 20 miles per hour when RPM is 3000. It seems the transmission does not up shift the gear, so it is always on the 1st gear. I went to Autozone and got the engine code P0720 which means the vehicle speed sensor circuit is opened or shorted, or there is something wrong with the vehicle sensor. However, I drove my car with very low speed to a nearby auto repair this afternoon. The people there said sensor seems OK, and let me go there to check again tomorrow morning. Did anybody meet this problem and solve it? Thanks.

[AZhitman]

Oil pedal? You mean accelerator pedal?

Sounds like your car is in "limp mode." Let's see if we can pull up some more info on that code - Hold tight.

[smart2003]

Oil pedal? You mean accelerator pedal?

Sounds like your car is in "limp mode." Let's see if we can pull up some more info on that code - Hold tight.

Yes, the accelerator pedal. Is that caused by transmission? Thanks a lot.

[AZhitman]

No, but it is caused by a bad sensor. Specifically, a bad vehicle speed sensor. It attaches to the transmission case and controls the shift points. Fortunately, it can easily be unbolted and replaced.

I would order the part from one of our vendors here (several carry OEM Nissan parts). Then, if you are comfortable using basic hand tools, we can walk you through the process of replacing it.

Alternatively, you can take it to the dealer, but you'll be paying full price for the part as well as the labor to replace it.

[smart2003]

Thanks a lot. Since I have made an appointment with a local transmission repair department, I will go there tomorrow morning anyway. If they can not fix it or charge too much. I am glad to accept your suggestion.

[smart2003]

No, but it is caused by a bad sensor. Specifically, a bad vehicle speed sensor. It attaches to the transmission case and controls the shift points. Fortunately, it can easily be unbolted and replaced.

I would order the part from one of our vendors here (several carry OEM Nissan parts). Then, if you are comfortable using basic hand tools, we can walk you through the process of replacing it.

Alternatively, you can take it to the dealer, but you'll be paying full price for the part as well as the labor to replace it.

Hi, I returned from the auto repair. They replaced the vehicle speed sensor, the problem still exists. So they think it is not caused by vehicle speed sensor. They reset the computer and let the two codes gone. Then the tire pressure light and service engine soon light are off, and car runs well. Therefore, they thought the problem is caused by the tire pressure sensor or bad circuit which confused computer and let it enter 'limp mode'. But I don't think this can solve my problem at all. How should I do it come back in several weeks. How does the tire pressure sensor work? Once the tire pressure is lower than a threshold, the tire pressure light will turn on? Or it will be on after several days. Anyway, if the tire pressure light turn on again, I will replace the bad tire pressure sensor.

[AZhitman]

I think you are right, and I think that shop needs to refund your money.

The tire pressure sensor (TPMS) isn't tied into the ECU (engine control unit) at all. You could have four flat tires, the vehicle won't enter limp mode. The TPMS units (one in each wheel) often go bad, but they won't cause the problem you describe.

I always advise people to buy their OWN scanner for OBD codes. You can get a decent one off ebay or Amazon... I have an Actron, like this: http://www.ebay.com/itm/ACTRON-OBD-II-A ... 1154219841

http://www.amazon.com/actron-code-reade ... 1383359917

[smart2003]

Yes, they just reset the computer and charged me $100 for it. They did check my car with their scanner and the result is no signal from secondary speed sensor (vehicle speed senor or revolution sensor in altima). So they thought that sensor is bad. However, after resetting the computer, the problem is gone. I am very afraid the issue may come back again, because they did not find the exact reason why my car entered limp mode.

[AZhitman]

For now, pay close attention to any strange noises or changes in driving dynamics. Get yourself a scanner (they also have cheaper ones that JUST give the code, which is fine). As soon as the code returns (if it does), then post it up and we'll walk you through the fix.

[smart2003]

Hi, you are right. The service engine soon light comes back. My car's speed is limited again.

One thing is interesting. If I start my car (the engine is started), there is only SES light on. However, if I put the car into ON without the engine started ( letting the car enter Diagnostic mode). There are 3 lights on, SES light, battery charge warning light and engine oil pressure warning light.

Do you have any suggestion? Do you know how to reset the ECU by myself? Thanks.

[AZhitman]

The lights are supposed to all come on when the key is in the ON position.

The only ones that matter are the ones that stay on while the car is running.

You still need to get a cheap scanner if you want to clear the codes, but the MOST important thing is to be able to READ the code. We need to know the exact code. The two possible replacement parts that will fix the problem are not expensive, and they're not hard to replace, but knowing what the code is (now) will help get it right.