Diagnosis and Repair
This section will cover common problems with PL vehicles, including diagnosis, testing, and correction. Please contact the author with any additional information or to request a new topic to be covered under this section.
Q: Is it possible to pull diagnostic trouble codes (DTC's) without a scan tool?
A: Yes, please CLICK HERE for more information!
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Diagnosis and Repair
Diagnosis and Repair
Last edited by OB on Fri Jun 17, 2011 1:01 am, edited 6 times in total.
Camshaft Position Sensor (CPS)
Camshaft Position Sensor (CPS)
By OB
This topic will cover diagnosis of intermittent failure of the Camshaft Position Sensor (CPS). Units have been known to fail both in low and higher mileage examples, and across most 2gn model/years. Note that the 03+ NGC cars seem especially prone to early failure. Located on the cylinder head, driver's side, the CPS uses a target magnet that indexes to the camshaft to determine camshaft position. This data is used by the PCM as a primary input for both fuel and spark control. Below is a symptom list used to diagnose a faulty CPS.
-Hard starting
-Crank No Start
-Limp Mode (Poor performance, limited revs)
-Check engine light (CEL)
-DTCs - Refer to list below
Here are all the possible related DTC's that can be associated with a failing or faulty CPS. Note that the most common is the P0340, which is a generic code that only means there is an unspecified issue with the signal sent to the PCM by the CPS.
-P0340 Camshaft Position (CMP) Sensor Circuit
-P0341 Camshaft Position (CMP) Sensor Performance
-P0342 Camshaft Position Sensor Circuit Low Input
-P0343 Camshaft Position Sensor Circuit High Input
-P0344 Camshaft Position Sensor Circuit Intermittent
Q: Why does the CEL go on and off? Why do CPS fault codes set and then disappear?
A: The reason the CPS code/CEL can go in and out is because the sensor is only failing intermittently. This means that the sensor only sends an 'erratic' signal to the PCM once in awhile. It might work fine for months in between triggering codes or a CEL. For example, if the CPS sends a random erratic signal to the PCM, the PCM will in turn set the necessary fault code. Depending on the severity (as determined by the PCM), a CEL and/or limp mode can be part of the measures to protect the engine and alert the driver of a possible severe problem. If the sensor starts acting normally again, the PCM will automatically reset the faults after it has seen xxx number of successful trips without a repeat. This process is the same for several other sensors that input info to the PCM, obviously with their own set of symptoms and codes.
How to fix the problem
The CPS issue can be very intermittent. Having said this, it is common practice to perform a PCM reset, clearing the code and CEL, thus temporarily 'fixing' the problem. I've seen some examples of cars that would set a code/CEL/limp mode, then after a reset, show absolutely no signs of CPS failure for several thousand miles of driving. On the other hand, such as with my own car, I could only go 10-15 miles between resets, sometimes much less. There is no way of knowing how your faulty CPS will act, so replacing the sensor the first time you have a problem with it is the best way to go.
If any of the above codes are setting, the ideal repair is to replace the CPS. If you are getting similar symptoms as the ones listed, but have no codes or CEL, I would recommend further diagnosis before replacing anything. Cam Position Sensors are available from both the dealer as well as local parts stores such as NAPA and Autozone. Regardless of where the sensor comes from, rarely have I seen an aftermarket or OEM replacement unit fail prematurely. It seems the original issue within the sensor has been rectified.
**Please direct all questions and comments to the author
By OB
This topic will cover diagnosis of intermittent failure of the Camshaft Position Sensor (CPS). Units have been known to fail both in low and higher mileage examples, and across most 2gn model/years. Note that the 03+ NGC cars seem especially prone to early failure. Located on the cylinder head, driver's side, the CPS uses a target magnet that indexes to the camshaft to determine camshaft position. This data is used by the PCM as a primary input for both fuel and spark control. Below is a symptom list used to diagnose a faulty CPS.
-Hard starting
-Crank No Start
-Limp Mode (Poor performance, limited revs)
-Check engine light (CEL)
-DTCs - Refer to list below
Here are all the possible related DTC's that can be associated with a failing or faulty CPS. Note that the most common is the P0340, which is a generic code that only means there is an unspecified issue with the signal sent to the PCM by the CPS.
-P0340 Camshaft Position (CMP) Sensor Circuit
-P0341 Camshaft Position (CMP) Sensor Performance
-P0342 Camshaft Position Sensor Circuit Low Input
-P0343 Camshaft Position Sensor Circuit High Input
-P0344 Camshaft Position Sensor Circuit Intermittent
Q: Why does the CEL go on and off? Why do CPS fault codes set and then disappear?
A: The reason the CPS code/CEL can go in and out is because the sensor is only failing intermittently. This means that the sensor only sends an 'erratic' signal to the PCM once in awhile. It might work fine for months in between triggering codes or a CEL. For example, if the CPS sends a random erratic signal to the PCM, the PCM will in turn set the necessary fault code. Depending on the severity (as determined by the PCM), a CEL and/or limp mode can be part of the measures to protect the engine and alert the driver of a possible severe problem. If the sensor starts acting normally again, the PCM will automatically reset the faults after it has seen xxx number of successful trips without a repeat. This process is the same for several other sensors that input info to the PCM, obviously with their own set of symptoms and codes.
How to fix the problem
The CPS issue can be very intermittent. Having said this, it is common practice to perform a PCM reset, clearing the code and CEL, thus temporarily 'fixing' the problem. I've seen some examples of cars that would set a code/CEL/limp mode, then after a reset, show absolutely no signs of CPS failure for several thousand miles of driving. On the other hand, such as with my own car, I could only go 10-15 miles between resets, sometimes much less. There is no way of knowing how your faulty CPS will act, so replacing the sensor the first time you have a problem with it is the best way to go.
If any of the above codes are setting, the ideal repair is to replace the CPS. If you are getting similar symptoms as the ones listed, but have no codes or CEL, I would recommend further diagnosis before replacing anything. Cam Position Sensors are available from both the dealer as well as local parts stores such as NAPA and Autozone. Regardless of where the sensor comes from, rarely have I seen an aftermarket or OEM replacement unit fail prematurely. It seems the original issue within the sensor has been rectified.
**Please direct all questions and comments to the author
Last edited by OB on Thu Jun 16, 2011 7:14 pm, edited 4 times in total.
Idle Air Control Solenoid (IAC)
By OB
This issue can be seen on almost all model years, and the problem seems more common in vehicles with manual transmissions. The IAC solenoid is located on the top of the throttle body. It controls airflow around the throttle plate to maintain idle, as well as aid in throttle tip-in and release. The solenoid is PCM controlled.
Symptoms
-Engine starts but dies immediately
-Engine starts but idles rough
-Engine cranks and sputters but does not start
Diagnosis
First, remove the IAC solenoid and clean it (see bottom of post). If this does not fix the problem, read on. If the engine responds to throttle input during cranking (or while running poorly), the IAC system is almost certainly the culprit. I've found that the plunger portion of the solenoid can get caught in its bore, causing a lack of IAC operation, or partial operation. I came across two additional DIY diagnostic tests that are fairly effective, in addition to the throttle test.
-Have someone crank the engine while you are standing over the engine. Tap the housing of the IAC solenoid with a deadblow hammer. This often frees up the plunger and returns normal operation to the solenoid. This is the same principle used with starter motors.
-Remove the IAC solenoid from the vehicle. Using a 12V power source, apply power and ground to the solenoid via the 2-prong connector. The plunger should snap into the full open position (as seen when looking through the outlet on the underside). In my experience, using full 12v power to exercise the solenoid will temporarily alleviate the issue. If the plunger does not open, replace the IAC. If it does, you can reinstall it and see if the problem persists, but there are no guarantees as to how long it will be before it happens again. A permanent fix would be to replace the IAC, however, it is unknown as to whether or not the new unit design has been revised.
Cleaning
An excessively dirty IAC should be removed and cleaned. This may not be related to this specific problem, but it's best to try this first. A dirty IAC can cause poor idle quality and reduce engine performance and fuel mileage if not kept clean. Use soap and water or light solvent and a lint free cloth to clean all aspects of the inner bore, mounting surfaces, etc. Gasket replacement is recommended but not required (per the 10+ times I've reused mine).
By OB
This issue can be seen on almost all model years, and the problem seems more common in vehicles with manual transmissions. The IAC solenoid is located on the top of the throttle body. It controls airflow around the throttle plate to maintain idle, as well as aid in throttle tip-in and release. The solenoid is PCM controlled.
Symptoms
-Engine starts but dies immediately
-Engine starts but idles rough
-Engine cranks and sputters but does not start
Diagnosis
First, remove the IAC solenoid and clean it (see bottom of post). If this does not fix the problem, read on. If the engine responds to throttle input during cranking (or while running poorly), the IAC system is almost certainly the culprit. I've found that the plunger portion of the solenoid can get caught in its bore, causing a lack of IAC operation, or partial operation. I came across two additional DIY diagnostic tests that are fairly effective, in addition to the throttle test.
-Have someone crank the engine while you are standing over the engine. Tap the housing of the IAC solenoid with a deadblow hammer. This often frees up the plunger and returns normal operation to the solenoid. This is the same principle used with starter motors.
-Remove the IAC solenoid from the vehicle. Using a 12V power source, apply power and ground to the solenoid via the 2-prong connector. The plunger should snap into the full open position (as seen when looking through the outlet on the underside). In my experience, using full 12v power to exercise the solenoid will temporarily alleviate the issue. If the plunger does not open, replace the IAC. If it does, you can reinstall it and see if the problem persists, but there are no guarantees as to how long it will be before it happens again. A permanent fix would be to replace the IAC, however, it is unknown as to whether or not the new unit design has been revised.
Cleaning
An excessively dirty IAC should be removed and cleaned. This may not be related to this specific problem, but it's best to try this first. A dirty IAC can cause poor idle quality and reduce engine performance and fuel mileage if not kept clean. Use soap and water or light solvent and a lint free cloth to clean all aspects of the inner bore, mounting surfaces, etc. Gasket replacement is recommended but not required (per the 10+ times I've reused mine).