6 replies to this topic

[redshift]

When I replaced the IAC valve some 6 months ago, I took the oportunity to blank off the EGR pipe from the manifold. As far as was known this shouldn't cause any problems for the ECU and certainly several thousand Km were covered without a hitch.

However, driving back from Nice last week the MIL lit up. Checking at home revealed:

P0401 EGR flow insufficient. (hardly surprising.....)
MIL status OFF

So MIL went off on the next re-start and clearly it was some kind of transient problem.

Anyone else seen this code?

[Rich H]

Spurious code, how would it measure EGR flow? There isn't anything I can think of.
Ignore and see if it pops back up?

[mike_sekinger]

Hi Pete,

Wayne Ellison encountered this code on his chargecooled V8. He did a very thorough investigation and we came to the conclusion that the low temperature threshold (interpreted as insufficient flow) had been triggered because the lower inlet temperature was cooling the egr sensor in the throttle body stack.

Wayne is in California, so he has to live with all of the smog compliance stuff (EGR, SAI) on this engine.

Did you leave the EGR temperature sensor connected to the loom? If so, I would disconnect it. If you do not have it connected, then I´m somewhat at a loss as to why you should be seeing that code.

Cheers,
Mike S

Edited by mike_sekinger, 06 September 2011 - 07:51 AM.

[redshift]

Thanks for the comments. I had left all of the wiring and sensors in place so that could explain where the ECU got the input from.
Not sure about a 'low temperature' connection as this occured on the A9 around Nimes, mid afternoon getting close to 40°! Even the coolant temp on the data was 91° which I don't see very often...

Sensor disconnection coming soon.

[mike_sekinger]

Agreed - in your case it is not likely to be a low inlet temperature triggering the error. As there are several components that impact the EGR temperature, I think you have triggered the error criteria with a freaky set of circumstances since the ECU is still commanding the EGR and receiving a temperature reading.

Disconnecting the EGR valve and the temperature sensor should solve the problem for you, premantly.

Cheers,
Mike S

[WEllison]

Hi Pete & Mike,

Like mike has stated, I have chased this problem on my intercooled and Federal smog compliant Esprit. The low temperature Mike is refering to is in a small chamber in the plenum after the throttle plates. The exhaust port, via the EGR valve, feeds this chamber as does the output from the IAC. Low flow is detected by the thermistor in this chamber indicating a low temperature. Somewhere below 150* F. In your case it will always be low, as the EGR path is blocked at the exhaust manifold. The thermistor resistance goes down as the temperature goes up. Unfortunitly you just can't just replace the thermistor with a resistor which makes the ECU think the temperature is just nice a hot. Becuase the ECU also detects the condition where the temperature is too high. I have not been able to determine a "middle ground" temperature/resistance which would keep the ECU happy. The error only occurs when the conditions are right to start the EGR self test, that's why you don't see it occuring to often. In my case the error only started after I had my ECU re-flashed, for an bug, by Lotus USA. My error eventually stopped occuring. I have theroized that the IAC finally found its non fast idle learning point and the cool air from my intercoolers, via the IAC valve, was finally reduced and the error stopped. As long as you have a smog compliant ECU with the EGR enabled I think you need to keep it functioning.

Wayne

[redshift]

Thanks for the complete description Wayne, that makes perfect sense.