I Checked the "code" from the Check Engine Light - OK, now what?

[ammcf1]

1994 3-cyl, 1.0 liter, automatic, 120,000 miles.

My Check Engine light has been on for a few days. The only "symptom" I have is that the temp. guage on the dash seems to be taking a very long time to warm all the way up (though when I initially begin driving it I go straight onto the highway for about 35 miles - and is has been pretty cold here. Could the natural airflow be keeping it cold?). Other than that the car is running great!

Today I followed the instructions given in this post to get the actual code. http://www.automotiveforums.com/vbul...t=check+engine

It's coming out to be either a 15 or a 51 (hard to tell which because there is the initial blink of the light when the key is turned and then it starts with 5, pause, 1, pause, 5 pause, 1, pause, etc. - I think...)

When I look it up here http://www.troublecodes.net/GMimport/ the 15 code shows as "Engine Coolant Temperature Sensor circuit Low Voltage Input. High temperature indicated." The 51 code shows as "EGR circuit."

4 questions:

1. Given my "symptoms" can anyone tell me which code is more likely?
2. Is there a way to tell which it really is short of having a computer diagnostic thing hooked up? (there's no auto shop in town that has one).
3. What steps should I take if it's a 15?
4. What steps shout I take if it's a 51?

Thanks for your help - you guys have helped me TONS with this car so far!

[91Caprice9c1]

You need to figure out which code it is. There is no way to tell which is more likely based on your long warm-up time because it is unrelated - that is a thermostat problem.

It can be tough to catch the first blink. It will repeat each code three times, then there will be a double-long pause before it repeats all the codes again. Try to catch the long pause - watch it for a few cycles if nessecary, you'll get the hang of it.

-MechanicMatt

[ammcf1]

OK, it appears to be the "51 - EGR circuit" - what do I do?

[GM Line Rat]

CODE 51 EXHAUST GAS RECIRCULATION CIRCUIT


DIAGNOSTIC AIDS
A poor or loose connection at the ECM could cause an intermittent failure. This could cause a DTC to be set falsely.

Closely check all vacuum hoses to the throttle body fuel injection (TBI) and the EGR valve. Also check the MAP sensor vacuum hose for leaks or restrictions. In "closed loop" operation with EGR enabled, the ECM will periodically turn "OFF" the EGR SV valve. If the corresponding manifold pressure change is less than a calibrated value, the ECM determines that a fault exists in the EGR system and sets a DTC 51.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

(1) This will check the circuit for a short to ground.
(2) Checks for voltage from FI relay.
(3) Checks the circuit for short to ground or a faulty ECM.
(4) Checks the circuit for an open GRN wire.
(5) A high resistance in the EGR SV valve could cause a Diagnostic Trouble Code (DTC) 51.


CIRCUIT DESCRIPTION
The Exhaust Gas Recirculation Solenoid Vacuum (EGR SV) valve is controlled by the Engine Control Module (ECM) . System voltage is applied to the EGR SV valve from the Fuel Injection (FI) relay. When the driver in the ECM closes, the EGR SV valve solenoid is activated.

Diagnostic Trouble Code (DTC) 51 will set if the following conditions are met:
System is operating in closed loop operation.
Manifold Absolute Pressure (MAP) is less than a calibrated value.

Trouble Code 51 EGR Checkout


EGR Control Circut


Service and Repair:
EGR CONTROL VALVE CLEANING

CAUTION: DO NOT wash any EGR valve in solvents or degreaser, as permanent damage may result, also, sand blasting of the valve is not recommended, since this can affect the operation of the valve.

CAUTION: Wear approved eye protection for this cleaning procedure, to avoid possible injury to the eyes.

Clean the control valve as follows:

Disconnect vacuum hose from EGR valve, then remove EGR valve-to-manifold retaining bolts, and the control valve.
With a wire wheel, remove the exhaust deposits from the mounting surface and around the valve.
Open the control valve, with an external vacuum source, and check for excessive buildup of carbon deposits. Anything more than a thin film is excessive.
Using a suitable sharp edged tool, scrape the carbon deposits from the control valve poppet. DO NOT scratch the valve seat or dislodge the poppet from its stem.
Check for wear of the poppet valve or stem, if any is noticed the control valve should be replaced.
Install new gasket, then install the control valve.
Reconnect the vacuum hose to the control valve.
INTAKE MANIFOLD CLEANING

NOTE: When cleaning intake manifold EGR passages, care should be taken to ensure that all loose particles are completely removed to prevent them from clogging the EGR valve or from being ingested into the engine.

CAUTION: DO NOT use drills or wires to clean carburetor control passages as calibration may be altered and result in poor engine performance.

Disconnect vacuum hose from EGR valve, then remove EGR valve-to-manifold retaining bolts, and the control valve.
Scrape carbon deposits from the EGR port using a suitable sharp edged tool. Use a wire wheel and brush all of the deposits off of the valve mounting surfaces.
Blow deposits from EGR ports and control passages using compressed air.
Install EGR control valve, using new gasket.
Reconnect EGR vacuum hose. Refer to MAINTENANCE SCHEDULES for service intervals.

[91Caprice9c1]

Excellent information sourced by GM.

The first thing I do when an EGR problem arises is manually open the valve, either with my fingers or carefully with a screw driver and a prying motion.


(This is NOT from a GEO METRO but the photo serves the purpose)

Start the engine and get it to operating temperature, then manually press the diaphram back toward the firewall, or carefully pry with a suitably sized screwdriver between the cage and the diaphram. This should cause the engine to stall within 5 seconds. If it does not stall, you have clogged passages/egr valve and can search for what people have done to clean them out. Moreover, if the car does stall your passages/egr valve are 'clear enough' and the problem is elsewhere and you should follow the flow chart offered by GM.

This is just my quick and dirty way to begin assesment of EGR function.

-MechanicMatt

[ammcf1]

I appreciate the thorough help... and I'm sure it will make more sense when I know this...

WHERE IS THE EGR VALVE? WHAT DOES IT LOOK LIKE?

Sorry, I'm not under the hood all that regularly

[91Caprice9c1]

Here is a view of the engine looking from the firewall toward the front of the car.




And a crude view from the front of the car.

If I had better pictures to source I would. But if you look at the pic of the valve in my previous post, yours will look very similar, and be in the location shown in these images.

-MechanicMatt

[ammcf1]

OK, MechanicMatt - I found the EGR and it does NOT stall when I do the screwdriver test you suggested. So, if I'm understanding correctly, I should take it off and clean it . Can you buy gasket material from the auto parts store and make your own, or do you have to buy one made for the application?

[91Caprice9c1]

Lots of info here about cleaning EGR passages and valves. A search will yield much savory information.

As for the gasket, you should use a pre-made gasket, special high temp stuff. $0.99 at all the autozones near me.

-MechanicMatt

[ammcf1]

Just to educate my ignorance - what does the EGR valve & system actually DO for the running of the car? (layman's terms, please).

Thanks

[GM Line Rat]

EGR (Exhaust Gas Recirculation) valve, It an Emmsions part. To clean the EGR Valve and EGR port in the intake manifold:

1). Buy a Large can of "Throttle Body" cleaner and a NEW EGR Gasket for your year of Metro.

2). Disconnect the NEG Battery cable 1st, then make note of the proper routing and placement for the EGR Vacumm
hose(s) to both the EGR Valve and the EGR vacumm Solenoid.

3.) Remove the vacumm hoses to the EGR Valve.

4.) Remove EGR bolts.

5.) Remove EGR valve and old gasket.

6.) Use a small phillips head screwdriver or pointed tool and push in gently on the center of the spring loaded EGR Pintle, then Spray liberally inside of the BOTTOM of the EGR valve with TB cleaner while facing the EGR Valve towards the ground to drain the cleaner and residue out. Use an old toothbrush or small scaper (Knife Tip) to clean around the pintle.

7.) Rinse good with TB Cleaner and make sure EGR Gasket surface is clean also.....Set EGR Valve aside to dry.

8.) Go to this link and read on how to clean the EGR Passages in the intake manifold! (2 Pages).

How do you clean the Carbon out of the Intake Manifold Gallery?

9.)When the cleaning is done, Reinstall EGR valve with the new Gasket, reconnect the vacumm hoses to the EGR Valve, Reconnect the NEG Battery cable. Start the car and warm it up, then check to see if code 51 Appears again or not? If it does......Further testing of the other EGR Components need to be done......Post back what you find after doing this cleaning!

[ammcf1]

The 51 code is gone! The EGR valve was STUFFED with the black carbon stuff. The second I took the hoses off, black stuff was sticking out of the small orifice. I went after the valve with the throttle body cleaner and got it all cleaned out as instructed. The passages in and out didn't seem too bad -though I did spray them pretty well with TBC too! Once I started it back up the 51 code was gone! And yes, I did let it get to operating temp and it still didn't show again!

Thanks so much MechanicMatt and GM Line Rat. You guys have once again saved me a BUNCH of head-ache (not to mention cash)!

[TENGRAM]

Originally Posted by ammcf1

Just to educate my ignorance - what does the EGR valve & system actually DO for the running of the car? (layman's terms, please).

Thanks

i'm incredibly late to this thread, but for posterity i figured would explain what the EGR does.

at part-throttle and when under load, the EGR system allows inert exhaust gas into your combustion chamber effectively taking up space that would otherwise be used for more air and fuel. less fuel means less heat and a smaller combustion event. this cooling effect also slows down (retards) the combustion event, which is why in EFI applications the ECM compensates by advancing timing when the egr is functioning. NOx formation occurs more rapidly at higher temperatures so the cooler combustion caused by the EGR reduces the amount of NOx emissions.

in short, EGR is a NOx reducer.