1994 N/A 850 - Recurring CEL (EGR flow too high in system)

[davhaney]

Hello friends. Longtime lurker, first time poster.

I have a 1994 N/A 850, 160k miles. I have replaced the entire PCV contraption, removed and cleaned the intake manifold, and cleaned the EGR valve itself thoroughly as well as the sensor. Additionally all vacuum hoses and elbows are tight, and accounted for. I still get occasional 1-5-4 code from A6, indicating "EGR Flow too high". Upon code clear, it returns. Sometimes 1,200 miles, sometimes 12 miles.

I recently removed the EGR valve again, and thoroughly cleaned it (yet again). On the bench, it did not seem to leak while closed-- and it would actuate correctly when I applied gentle vacuum to the diaphragm side. This component is shiny and clean. Re-installed, cleared code, and CEL came back on 22 miles later. Reports A6 code 1-5-4 (again).

If we assume the EGR valve is okay, what else do I need to look at? Is the CEL triggered by excessive heat on the sensor, when EGR isn't called for? Could it be that sensor reporting incorrectly? Could the servo which opens the vacuum circuit be sticking in the open position (therefore opening the EGR valve whenever the car is on)? Has anyone seen this before?

Your thoughts and opinions are all valued. I would have contributed on this forum previously, but whenever I search for problems, they're all solved!

[Ozark Lee]

The 1-5-4 code is actually the temperature sensor getting to low of a reading which the ECU interprets as the exhaust flow being to low.

From the book:

1-5-4 (EGR System Leakage)

1) Symptom of EGR system leakage is rough idle. Code will set when engine temperature is 150 F (65 C) or less, and temperature sensor detects an increasing temperature. If ECU detects that temperature of EGR temperature sensor varies by more than a preset limit before temperature has reached 150 F (65 C), ECU will interpret condition as an EGR flow and will initiate a code. Some faults that can produce this code include:

Leaking EGR valve.
Signal to EGR controller faulty.
EGR controller defective.
Poor ground.
Engine thermostat defective.

2) Start engine and listen to idle. If idle is okay, go to step 4) and check engine temperature. If idle is not okay, disconnect
EGR controller connector. If idle is still rough, go to next step and check EGR controller. If idle is now okay, check Green/Brown wire between ignition ECU terminal for a short to ground.

3) To check EGR controller, run engine at idle. Carefully disconnect Yellow hose from EGR controller. If idle is now okay,
repeat test using new EGR controller. If idle is still rough, turn ignition off. Carefully disconnect Yellow hose from EGR valve. Check hose for blockage or leaks. If Yellow hose is okay, repeat test using new EGR valve. If hose is blocked or leaking, replace hose. In both cases, clear codes.

4) Check engine temperature gauge with engine running. If gauge pointer does not rise to normal and top radiator hose is hot, go
to next step. If gauge shows normal operating temperature and top radiator hose is hot, go to step 6). If gauge pointer rises slowly and top radiator hose is not at normal operating temperature, retest system using new thermostat. Clear codes.

5) Turn ignition off. Disconnect Mass Airflow (MAF) sensor connector. Connect an ohmmeter between MAF sensor connector terminal No. 2 and ground. See Fig. 5. If ohmmeter indicates about zero ohms, go to next step. If ohmmeter does not indicate about zero ohms, disconnect electrical connector located under intake manifold, on engine block. Clean and reconnect connector. Clear codes.

6) Code may be set by contact resistance at EGR and engine temperature sensor connector. Clean and protect EGR and engine
temperature sensor connectors from oxidation, dirt, etc. Clear codes.


...Lee

[davhaney]

Lee -

For some reason, I thought A6 1-5-4 was EGR too high. Thank you for correcting me. Testing shows no vacuum at the EGR diaphragm. Tracing back, I show 12 volts being applied on the EGR Controller, showing it's calling for vacuum (I think). Testing the EGR Controller, I show an open circuit.

My next step will be to replace the EGR Controller, and test once again. Thank you so much for your time.

[davhaney]

Following up, replacement of the EGR Controller unit positively solved the issue. Thank you!

[loveMy850]

I get a rough idle in drive, could it be EGR controller, how do I check that, have no one to sit in drive, has to be check in park could I possibly still see a difference.ty