Trying to diagnose 99 Toyota EGR low flow and need better ELM327 scan tool software

1999 Toyota Camry. There is a code for Exhaust Gas Recirculation insufficient flow detected. The EGR exhaust tube is not blocked and the EGR valve operates when I operate it (not necessarily when the ECU commands it to operate). Opening the EGR valve with my hand when it’s idling will make the engine stall.

So I need a way of testing associated electronics. I need to command the computer to open the EGR valve, and also the tube (not the one to the VSV) that goes out the side of the EGR valve over to some other thing with hoses needs to be tested. That must be the sensor that measures pressure to see if there’s flow.

I have the ELM327 scan tool but none of the software that came with it has any vehicle specific diagnostics. No ABS, no airbag, nor any way to command the computer to do things like operate the ABS unit to test the channels, nor any way to open and close the EGR valve (even if it stalls the engine I’ll know if that’s working or not), or give me a read out on what ever pressure sensor is there to verify ERG functionality. No way to directly operate the EVAP valves to test that.

Even if I fix the EGR problem I still need better software or commands to type in the console to do these vehicle specific OBD2 things. What software is out there?

No experience w/99 Camry, but my 92 Corolla probably uses a similar EGR design. Maybe I can provide a little help w/how it works. Two components, EGR valve, and EGR modulator. The EGR valve isn’t like an evap purge valve, either open or closed; instead the EGR valve is generally somewhere in between, i.e. partially open. The main input deciding how much to open is the amount of exhaust flow. The more exhaust flow, the more it opens. There’s no computer involvement w/that, done using a gadget (I believe it is on the EGR modulator) sensing the exhaust pressure, ad causing the valve to open an amount corresponding to that pressure.

The other input controlling the EGR valve comes from the computer, implemented via a vacuum switching valve. That’s just a electric-solenoid controlled valve in the vacuum system that’s either open or closed, open/closed decided by computer. It’s purpose is to over-ride the exhaust gas flow input (above), and keep the EGR valve 100% completely closed (no EGR) in certain situations. For example if coolant temperature too low, EGR could stall engine. Or with wide open throttle you don’t want any EGR b/c if you are flooring the gas pedal you want all the power the engine can provide, might be passing an 18 wheeler on 2-lane road w/on-coming traffic.

The other computer involvement is the EGR flow sensor. On my car that’s only used on California-destined cars, but may be used on all cars by 1999. Used to verify the valve is actually opening when the computer thinks it should. The sensor is just a thermistor (a resistor whose resistance varies with temperature), and the computer measures its resistance to determine the temperature. It’s located on the EGR passage, so when the valve opens it should get hot b/c exhaust gas is hot. The code ( Exhaust Gas Recirculation insufficient flow detected) means it isn’t getting hot like it should, when it should. So most likely either the sensor is faulty, the electrical connection between computer and sensor is faulty, EGR valve or modulator is faulty, or the EGR passage is partially obstructed. You’ve apparently verified the EGR valve will stall engine when it is open, so that means the passages must not be obstructed. I’m guessing either the thermistor has failed or there’s a problematic electrical connection from the sensor to the computer. First test imo is to measure the sensor’s resistance.

Thanks for your reply. I’ll look in to what must be the modulator that is off to the side of the EGR valve.

That modulator is also known as a back-pressure transducer. If you place the transmission in drive, apply the brake and open the throttle, the modulator should allow vacuum to the EGR valve.

Good chance the modulator diaphragm is dirty or leaking. Some can be disassembled and cleaned.