P0488 – Exhaust Gas Recirculation (EGR) System Throttle Position Control Range/Performance

By Stephen Darby (Contact Me)
Last Updated 2016-10-09
ASE Master Tech

Table of Contents

1. What Does Code P0488 Mean?
2. What are the common causes of code P0488 ?
3. What are the symptoms of code P0488 ?
4. How do you troubleshoot code P0488 ?
5. Codes Related to P0488
6. Get Help with P0488

What Does Code P0488 Mean?

A stored code P0488 means that the powertrain control module (PCM) has detected a discrepancy between the actual position of the exhaust gas recirculation (EGR) valve and the desired throttle position.

The PCM uses input signals from the throttle position sensor (as well as the vehicle speed sensor and other engine sensors) to determine the desired percentage of EGR valve activation at any given time and under a particular circumstance.

There are two basic types of EGR valves; linear and vacuum diaphragm. Both types are controlled by the PCM in different ways.

The linear EGR valve is opened using one or more servo motors that are directly attached to the EGR pendulum. The PCM not only controls EGR valve function, it also monitors manifold absolute pressure (MAP) and exhaust oxygen content to determine whether or not the EGR is functioning properly. Some EGR valves are also equipped with valve position sensors which reflect (to the PCM) the percentage in which the valve is actually opened.

The vacuum diaphragm EGR valve is also controlled by the PCM but engine vacuum is used for opening. Typically, an in-line (intake vacuum) vacuum control solenoid is provided a voltage signal when the engine is running. When the PCM deems that EGR operation is feasible, a fluctuating ground is applied to the solenoid; causing it to open and allow a percentage of engine vacuum to reach the EGR valve. The EGR valve should open accordingly and the PCM looks for MAP changes that reflect such.

The typical TPS is a potentiometer that is moved along with the throttle plate. A five-volt reference circuit is completed by the TPS. As the throttle plate is opened, sensor resistance decreases, allowing circuit voltage to increase. The PCM recognizes these variations in TPS voltage as changes in throttle position. TPS signal voltage normally ranges from .5-volts at idle to 4.5-volts at wide-open throttle.

As the PCM monitors changes in MAP and exhaust oxygen content (in relation to the EGR system), data is compared to the throttle position sensor. Variations between perceived EGR system performance and TPS position, over a set period of  time, will result in a stored code P0488 and possibly an illuminated malfunction indicator lamp.

What are the common causes of code P0488 ?

• Clogged EGR passages
• Defective EGR valve
• Bad EGR (or DPFE) sensor or sensor hoses
• Open or shorted EGR or TPS circuits or connectors
• Defective or misadjusted TPS

What are the symptoms of code P0488 ?

• There is a very good chance that no symptoms at all will be presented
• Rough idle or engine stall at idle (EGR valve is stuck open)
• Other EGR efficiency and/or TPS codes may accompany this code

How do you troubleshoot code P0488 ?

I would gain access to a diagnostic scanner, a digital volt/ohmmeter (DVOM), a hand-held vacuum pump, and a reliable vehicle information source (All Data DIY is a great one) to diagnose a code P0488.

I would begin with a visual inspection of EGR and TPS related wiring harnesses and connectors. I would pay particular attention to high temp hoses for the DPFE sensor for the EGR (if applicable). Consult your vehicle information source for related technical service bulletins. If there are any, use the information to help in your diagnosis.

Connect the scanner to the diagnostic port of the vehicle and retrieve the stored codes and freeze frame data. Writing this information down may prove helpful later. Now clear the codes and test drive the vehicle.

If the P0488 code is reset, accompanied by other EGR related codes, test EGR system efficiency. If the vehicle has a linear EGR valve, use the scanner to activate the EGR valve and observe the appropriate data inputs to determine if it is functioning properly. The vacuum diaphragm EGR valve can be tested using the hand-held vacuum pump. With the engine started and idling, disconnect the vacuum hose from the EGR valve and apply the appropriate amount of vacuum using the hand-held vacuum pump. With vacuum applied to the EGR valve, the engine should stall. If it doesn’t, suspect a defective EGR valve or clogged EGR passages. Clogged passages are far more common than faulty EGR valves.

To determine whether the EGR valve is bad or the passages are clogged, turn the ignition off; remove the EGR valve and apply vacuum to it. Look and see if the pendulum is opening when vacuum is applied. If it is not, the EGR valve is defective. If the pendulum is open, start the engine. The engine should stall due to the massive vacuum leak caused by the open EGR port. IF the engine idles normally, you have clogged EGR passages. EGR passages can be cleaned in several different ways, consult your vehicle information source for the manufacturer’s recommended method.

If the code is reset, accompanied by other TPS codes, use the DVOM to test TPS signal voltage. With the DVOM test leads connected to the appropriate circuits (see the vehicle information source), observe live data while actuating the throttle plate. Voltage should steadily increase as the throttle is opened and decrease as the throttle is allowed to close. Voltage should increase and decrease through the entire throttle curve without glitches or hiccups. If it doesn’t, replace the TPS.

Codes Related to P0488

• P0120 Throttle Position Sensor/Switch A Circuit Malfunction
• P0121 Throttle Position Sensor/Switch A Circuit Range/Performance Problem
• P0122 Throttle Position Sensor/Switch A Circuit Low Input
• P0123 Throttle Position Sensor/Switch A Circuit High Input
• P0124 Throttle Position Sensor/Switch A Circuit Intermittent
  P0220 Throttle/Petal Position Sensor/Switch B Circuit Malfunction
• P0221 Throttle/Petal Position Sensor/Switch B Circuit Range/Performance Problem
• P0222 Throttle/Petal Position Sensor/Switch B Circuit Low Input
• P0223 Throttle/Petal Position Sensor/Switch B Circuit High Input
• P0224 Throttle/Petal Position Sensor/Switch B Circuit Intermittent
• P0225 Throttle/Petal Position Sensor/Switch C Circuit Malfunction
• P0226 Throttle/Petal Position Sensor/Switch C Circuit Range/Performance Problem
• P0227 Throttle/Petal Position Sensor/Switch C Circuit Low Input
• P0228 Throttle/Petal Position Sensor/Switch C Circuit High Input
• P0229 Throttle/Petal Position Sensor/Switch C Circuit Intermittent
• P0400 Exhaust Gas Recirculation Flow Malfunction
• P0401 Exhaust Gas Recirculation Flow Insufficient Detected
• P0402 Exhaust Gas Recirculation Flow Excessive Detected
• P0403 Exhaust Gas Recirculation Circuit Malfunction
• P0404 Exhaust Gas Recirculation Circuit Range/Performance
• P0405 Exhaust Gas Recirculation Sensor A Circuit Low
• P0406 Exhaust Gas Recirculation Sensor A Circuit High
• P0407 Exhaust Gas Recirculation Sensor B Circuit Low
• P0408 Exhaust Gas Recirculation Sensor B Circuit High
• P0409 Exhaust Gas Recirculation Sensor “A” Circuit

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