You may also find a P0300 "random misfire" code. Rough idle or misfiring because the EGR valve is not closing and is leaking exhaust into the intake manifold. The fix here is to inspect the EGR system, remove the EGR valve and check the valve and port for carbon, and remove the carbon from the port if it is plugged. Pinging (spark knock or detonation) because the EGR system is not working, the exhaust port is plugged up with carbon, or the EGR valve has been disabled. See the Mode 06 Diagnostics section for more info. This may take several drive cycles to occur. If a component is acting up, it will FAIL the self-test - but it may not set a DTC unless all the other failure criteria for the DTC have also been met. When you go to the Mode 06 menu, you can see the OBD II self-test data for all the EGR components and can tell at a glance whether they are operating in or out of range. Most scan tools can access a menu called "Mode 06." You will usually find this by choosing "global" or "generic" OBD II on the scan tool main menu rather than entering the vehicle year, make and model.
Ecu diagnostics menu update#
This requires a Tech 2 scan tool and a software update from GM. The cure, in this case, is not to replace the EGR valve but to reflash the PCM with new programming instructions that allow a longer response time from the EGR valve. It still works and keeps NOX emissions within acceptable limits, but the computer thinks the EGR valve is not opening quickly enough and sets a code. When the computer commands the EGR valve to open, it wants to see a movement signal from the EVP sensor within a certain number of milliseconds (typically 50 ms or less).īut as the EGR valve ages, it may not open as quickly as it once did.
Ecu diagnostics menu code#
The P1406 code indicates an EGR problem, but replacing the EGR valve won't fix it because the real problem is that the OBD II system's self-diagnostics are overly sensitive. On some 1995 and newer GM vehicles with OBD II and linear EGR valves, the MIL light may come on and set a Code P1406 when the engine has high mileage on it. The voltage signal typically varies from 0.3 (closed) to 5 volts (open). The sensor works like a throttle position sensor and changes resistance. The EVP sensor also helps with self-diagnostics because the computer looks for an indication of movement from the sensor when the it commands the EGR valve to open or close. Linear EGR valves may also be equipped with an EGR valve position sensor (EVP) to keep the PCM informed about what the EGR valve is doing. The further the valve opens, the greater the flow rate.
"Linear" EGR valves use a motor to open the valve. If an engine has an electronic EGR valve, the PCM operates the valve by energizing a motor or solenoids. The solenoids are normally closed, and open only when the PCM completes the ground to each. The PCM varies the flow rate by energizing various combinations of the solenoids. Each has a different sized valve (small, medium and large). "Digital" EGR valves have several solenoids (two or three in the case of GM). Inceasing the "on time" of the solenoid holds the valve open longer and increases the flow rate. The PCM may cycle the solenoid on and off to vary the EGR flow rate. If teh engine has a vacuum-operated EGR valve, the PCM controls a solenoid in the vacuum line to open and close the valve. On most OBD II vehicles, the EGR valve is controlled by the powertrain control module. If it is not, it can make for hard starting when the engine is cranked.
The EGR valve should be fully closed when the engine is off. It should only occur after the engine has warmed up and is running at a speed above idle. It should NOT occur when the engine is cold because it acts like a vacuum leak and can cause a rough idle or lean misfire.ĮGR also should also NOT occur at idle for the same reason. MORE ABOUT THE EGR SYSTEMĮxhaust gas recirculation is only a part-time function.
Ecu diagnostics menu portable#
NOX emissions are highest when the engine is under load, which means you may not be able to get accurate readings unless the vehicle is tested in a "loaded mode" by driving it on a dyno, or using a portable exhaust analyzer while test driving the vehicle on the road. The only way to know for sure is to check NOX emissions with an exhaust analyzer. It might be producing elevated levels of NOX in the exhaust if the EGR system is not operating correctly. Some systems also have an EGR valve positon sensor to monitor the opening and closing of the EGR valve.Ĭode for EGR-related faults include P0078 to P0086, and P0400 to P0409.Īn EGR-related fault code does NOT mean the vehicle is polluting. OBD II may check for a drop in intake vacuum through the MAP sensor when it commands the EGR valve to open. The EGR system reduces the formation of oxides of nitrogen (NOX) in the exhaust when the engine is under load. On some vehicles, the OBD II system may monitor the operation of the exhaust gas recirculation system.
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