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07 Malibu engine power reduces to limp mode

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I have an 07 Chevy Malibu 2.2 4 cylinder. Today with the cruise set, the check engine light came on and power was reduced to a 40mph limp mode. I pulled off the road, where at idle it shook like there was a bad misfire, and I shut her off. I checked a few things, disconnected negative terminal on battery, hooked back up, and restarted the car. Check engine light disappeared, and car ran fine. Headed back down the road, cautiously. 10 miles later with cruise engaged, it all happened again. Cruise disengaged, check engine light came on, and it only rev up if car was under 40 mph no matter what I did with gas pedal. Limped for a few miles to a wayside rest, and at idle speed, it chugged again, so I put in neutral, shut it off, and coated into a parking spot. Text a friend down the road, to get him on the way with his car trailer. He showed up, car started up, ran fine, but drove it on the trailer. Any thoughts? Throttle body issue maybe? I know I can scan it this week with the engine light on, but thought I'd pick your guys brains and have issue resolved.

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I had very similar symptoms with my 05 f150 recently. I checked the throttle body and it was filthy. Gave it a good cleaning and it has ran fine since.

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If it's anything like the Impala, it could be a throttle position switch (?) by the gas pedal that is malfunctioning.

Jeremy can confirm whether or not this switch exists or it's proximity on the vehicle.

My mother inlaw had the exact issue with her Impala.

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If it is drive by wire than the throttle pedal is the "app" there are two APP sensors in the throttle pedal assemble. One is low and one is high. As you press down on the pedal the low goes to high and the high goes to low. If there is any mismatch in the two signals the ECM will go into a limp mode. The same is true for the throttle position sensors. There are also two of these and they also act the same way as the APP sensors.

GM drive by wire in the a malibus is a plagued system. Everything from the throttle pedal, TAC, and wiring is a suspect when the right codes are present.

On a side note the newer drive by wire TAC (throttle body) no longer have a voltage value for the throttle position sensors. GM has developed SENT (one way communication network). With SENT both throttle position values are converted to a 5 volt coded digital signal. That signal is sent to the ECM via one wire. What does this mean? The signal is no longer measurable via a volt meter. Even with a lab scope watching the signal there is no way to interpret the coded message. This is just the start GM has plans to incorporate this technology into other sensors.

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If it is drive by wire than the throttle pedal is the "app" there are two APP sensors in the throttle pedal assemble. One is low and one is high. As you press down on the pedal the low goes to high and the high goes to low. If there is any mismatch in the two signals the ECM will go into a limp mode. The same is true for the throttle position sensors. There are also two of these and they also act the same way as the APP sensors.

GM drive by wire in the a malibus is a plagued system. Everything from the throttle pedal, TAC, and wiring is a suspect when the right codes are present.

On a side note the newer drive by wire TAC (throttle body) no longer have a voltage value for the throttle position sensors. GM has developed SENT (one way communication network). With SENT both throttle position values are converted to a 5 volt coded digital signal. That signal is sent to the ECM via one wire. What does this mean? The signal is no longer measurable via a volt meter. Even with a lab scope watching the signal there is no way to interpret the coded message. This is just the start GM has plans to incorporate this technology into other sensors.

You just need a logic analyzer. Turns out that ones that plug into PC have gotten cheap. Here is an example.

http://www.linkinstruments.com/logicanalyzer.html

They are used for debugging digital systems.

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You just need a logic analyzer. Turns out that ones that plug into PC have gotten cheap. Here is an example.

http://www.linkinstruments.com/logicanalyzer.html

They are used for debugging digital systems.

You can look at the pattern on a lab scope. There is no way of "interpreting" the data. So for instance. At "closed throttle" there will be a distinct pattern of "on" and "off" (0-5 volt square wave). For example you can interpret it as 10010101001010010 (1 = 5 volts 0 = 0 volts). That pattern will change as the throttle is opened. There is no way to interpret the data or patterns to decipher what position the throttle body is in other than what the ECM is decoding and sending to the scan tool. Traditionally you would be able to use a multi-meter and read voltages produced by the sensor (1.4 volts to 4.9 volts, roughly, depending on the position on the throttle).

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So your friends at GM don't tell you what the data stream format is? Two start bits one stop bit, etc? Nice guys. They going to sell a special tool?

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Did you figure anything out? As was stated above, the very first step is to read the code(s). There is no point speculating before doing that. You can get a basic OBD II code reader quite cheap these days. Like under 30 bucks. Several things will make a Malibu or other GM cars go into limp mode, along with Chryslers. I am not familiar with Fords. You need the code to know where to start, since it could be a totally different area than you're thinking, such as camshaft/ crankshaft position sensors, or even issues with O2 sensors.

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Sorry for my delayed response. I work on the road during the week. Just got around to tinkering today full-18473-54923-image.jpg

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Both refer to teh throttle actuator. In earlier model years there was even a tsb for if it keeps coming back.

google malibu p1516 for bunch of articles.

Here is a quote from one...

Quote:
1. This engine uses the Throttle Actuator Control (TAC) system. Thoroughly clean the throttle bore and throttle plate.

2. Inspect the air intake system for a missing or contaminated air filter

there is also a tsb on it TSB 07-06-04-003 for p1516 that involves replacing the pcm

--------------

P1516 Chevrolet Comments | Add Comment

Possible causes

- Faulty Throttle Actuator Control (TAC) module

- Throttle Actuator Control (TAC) module harness is open or shorted

- Throttle Actuator Control (TAC) module circuit poor electrical connection

- Check Throttle Actuator Control (TAC) module connector for water

- Binding or bent throttle plate-failed throttle body

What does this mean? What does this mean?

Tech notes

What does this mean? What does this mean?

When is the code detected?

The Engine Control Module (ECM) has detected an out of range condition between the predicted and actual throttle position.

Possible symptoms

- Engine Light ON (or Service Engine Soon Warning Light)

- No throttle response

P1516 Chevrolet Description

The Engine Control Module (ECM) is the control center for the Throttle Actuator Control (TAC) system. The ECM determines the drivers intent and then calculates the appropriate throttle response. The ECM achieves throttle positioning by providing a pulse width modulated voltage to the TAC motor. The TAC system uses the following circuits for Motor control 1 and Motor control 2.

Two processors are also used to monitor the TAC system data. Both processors are located within the ECM. Both processors monitor each other's data to verify that the indicated throttle position is correct.

That was two. Here is another

Quote:

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:

As carbon builds up in the throttle body of a high mileage vehicle, the ECM/PCM learns to compensate by increasing the throttle plate angle.

If enough carbon builds up, an idle surge, deceleration surge, tip-in hesitation, reduced engine power mode, and/or DTCs P0068, P0121, P1516, P2101, P2119, and/or P2176 may be experienced on high mileage vehicles.

If the throttle body is cleaned without performing an "idle learn reset/reset idle learn" with the Tech 2, the ECM/PCM may continue to compensate for previous carbon build up, causing it to return with a similar concern as well as DTCs P0121, P0506, and/or P0507.

In a similar fashion, if the ECM/PCM of a high mileage vehicle is replaced and/or reprogrammed without performing the Throttle/Idle Learn outlined in SI, the ECM/PCM may no longer compensate for existing carbon build up in the throttle body, causing it to return with a similar concern as well as DTCs P0121, P0506, and/or P0507.

Recommendation/Instructions:

If SI diagnosis does not isolate the cause of this concern, inspect the throttle body bore and plate for obvious carbon build up.

If carbon is present, follow the Throttle Body Cleaning Procedure in SI to clean the throttle body.

After ensuring that the throttle body bore and plate are clean, perform an "idle learn reset/reset idle learn" with the Tech 2 and re-evaluate the concern.

Notice: Depending on the vehicle you are working on, the "idle learn reset/reset idle learn" is normally found on the Tech 2 ECM menu for Module Set Up or Special Functions/TAC System.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

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