AMM checking - a How To (Very Long) - Saab 9000 Bulletin Board - Saabnet.com
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AMM checking - a How To (Very Long)
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Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Thu, 17 Mar 2005 06:34:22 Share Post by Email
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I've dug up this information from various Saab manuals, most notably 2:3, LH Injection System. Hopefully it'll help address AMM questions.

What got you here-
The Check Engine light came on, and or poor driveability, hard starting, high fuel consumption, slow off-the-line performance, and/or the engine seems to ignore your accelerator inputs.
Fault codes (from ISAT) – 45641/25641, 45651/25651, 45691/25691.
Lamp-Flash code – 12221
LH system Test – E207, E107, E007.

Identify your quarry-
AMMs come with two body styles – Aluminum and Plastic. In general, Aluminum is 1987 and earlier N/A, 1988 and earlier Turbo. Naturally, Plastic is 88 and later N/A, 89 and later Turbo. The Aluminum AMM has an adjusting screw, the Plastic body does not. Exception – In non-catalytic converter markets, the 88-90 LH2.2, and all 2.4.2 have a plastic AMM WITH an adjusting screw – again, non-cat cars only. Let’s call them AL for aluminum, P for plastic with no adjustment, and PX for plastic with adjustment.
Note- The three types are NOT INTERCHANGEABLE. Well, not if you want it to work. Saab documentation says that damage to the LH module will occur if you put the wrong one in. So don’t.

Step 1 – unplug the AMM connector. Check that the pins in the connector and AMM are free from corrosion. Otherwise, clean with contact cleaner, but if the pins are corroded, there is a good chance the internal circuit board is corroded, and that will require AMM replacement. Check that the wire screens on either end are intact and clean. Look to see that the thin platinum wire is intact – do not touch it or try and clean it.
If you have an AL or PX sensor, take out your ohmmeter, and measure across pins 3 and 6 (AL) or 2 and 6 (PX). For type P skip this step. You should get a resistance reading in the 100-1200 ohm range. If you turn the adjustment screw, the resistance should change. Turn it back to where it was, unless you will be adjusting the AMM. If the resistance is an open circuit, or it doesn’t change when you turn the screw, the AMM is bad.

Step 2 – Measure resistance on the harness side of the AMM connector from pin 4 (AL) or pin 1 (P, PX) to ground. It should be only a couple of ohms. If not, there is a wiring problem or a bad ground. Change the meter to volts, and measure pin 2 (AL) or pin 5 (P, PX) to ground. Turn the key to ON. You should see battery voltage. If not, there is a problem with the wiring to the AMM, or with the main relay. Check for continuity between pin 2/5 with pin 87B of the main relay.

Step 3 - Burn-Off. Put the AMM back in place, with the connector on. Start the car and let it idle to warm it up. It should get to 150F, which is the temp gauge up off the peg. Shut off the engine, and unplug the front (air filter) side of the AMM. You will be running the engine without the air filter, so try and avoid dusty days and keep small animals away from the intake. Restart the engine and let it idle for a bit. Rev the engine to 2500 rpm. It doesn’t have to be exactly 2500 rpm, you just need to be sure you get over 2100 rpm. Let it return to idle. If you have a LH2.2 car (AL, some PX), you’ll need an assistant; with LH2.4 and later (P and some PX,) you should be able to do this yourself. Shut the engine off and look into the throat of the AMM. About 20 seconds after shut-off (LH2.4 and up), you should see the wire glow brightly for about a second. For LH2.2, you have only 4 seconds after shutoff, so unless you’re REALLY fast, have an assistant shut off the engine.
If it glows brightly (Burn-off), go to Step 4. If not, unplug the electrical connector, and re-connect the AMM to the air filter hose (no need to risk ingesting stuff). Start the engine – you may get a CEL because the AMM is disconnected, and it may not run very well. Let it warm up. Rev the engine to 2500 rpm – it may stumble - press the gas pedal slowly. Let it return to idle. Measure the voltage between pins 1 and 4 on the connector on the harness (not on the AMM). Shut off the engine. 20 seconds after shut-off (P, PX), the voltage should go up to about 4 volts for 1 second. (4 second delay for AL).

If you get the 4 volts AND the filament didn’t glow, replace the AMM. If you don’t get the 4 volts, unplug the connector from the LH ECU. You should have continuity between pin 1 of the AMM and pin 8 of the ECU for AL; for P and PX, it is pin 4 of the AMM and pin 8 of the ECU. If the continuity is good, then the problem is in the LH ECU.

Step 4 – Measure continuity. Unplug the LH ECU connector. For AL, you should have continuity between the AMM connector pin 3 and LH pin 6, and AMM pin 5 and LH pin 7. For P and PX, measure continuity between AMM connector pin 2 and LH ECU pin 6 and AMM pin 3 and LH pin 7. Burn-off was covered in step 3. If you don’t get continuity (around 1-2 ohms), check the wiring. Plug the LH ECU connector back in.

Step 5 – You need to be able to access the back of either the AMM or LH connector – the AMM is best. This must be done with the AMM connected up. Carefully peel back the rubber. Set the meter to volts, and measure on the AMM connector between pin 5 (AL) or pin 3 (P, PX) and ground. With the car ON, but the engine not running, you should see 1.2 to 1.5 volts. Start the engine. The voltage should still be around 1.2-1.5 volts with the engine at idle. Rev the engine – the voltage should increase. Expect near 5 volts for wide open throttle. Voltage should increase with increased airflow (revs). If you don’t get these voltages, the AMM is suspect.


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