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NO START CHECKS 2.4 LH

First, anytime testing is done at the ECU, unless otherwise stated, make sure the ECU is unplugged. Unplug the ECU only when the key is off. This avoids any possible spikes. Make all measurements, probes, from the back of the connector to avoid damage to the female pins. Check all connectors for pushed out or corroded pins, often the cause of problems. Never take a resistance reading (ohms) on a live circuit or a circuit connected to the ECU. Doing so could cause damage to the ECU or the ohmmeter. Ohmmeters measure resistance by sending a current they produce through the wiring. This current can damage unprotected computer circuits. For this reason, make sure the computer is unplugged before taking resistance readings. It is best to use an very high impedance meter to avoid damaging fragile circuits. See your meter specs for its impedance, Saab recommends at least 20000 ohm/V internal resistance for analog meters. Trying to read resistance on an unisolated circuit can give false results, if you get a bad reading while checking resistance, refer to a wiring diagram and insure you are measuring an isolated circuit, not one with parallel branches .

• Make sure there are no major intake leaks in between the air mass meter and the throttle body. On turbos, this will require inspection of all the intake tubes and rubber pieces. On 9000s with two piece manifolds, make sure the rubber sleeves are intact and not separated or have loose clamps. Check the turbo bypass valve, the PCV system, all vacuum hoses, the vacuum reservoir and the charcoal canister system. Make sure none of the grommets or ports in the intake have popped out.
• Fuel. Make certain that the car has gas in it. On these pre pump/fuel canister systems, at least two gallons of fuel are required to prime/fill the canister.
• Check the fuses. All of them. Sometimes a fuse critical to a system is not labeled as protecting it.

900 Fuel pump fuse A) Key On Signal A) Coil Primary ) All these are in the engine compartment fuse/relay box.

9000 Fuel pump fuse A) Key On Signal A) In the glove box fuse compartment    Coil Primary ) 88-> in the engine compartment fuse/relay box.

• Check for spark at the coil. Use an old plug and ground its electrode and crank the engine over watching for spark across the gap. If the tach bounces while cranking, the primary circuit and the ignition amp are all working. An inductive timing light can be used to verify spark as well. If using an old plug, open its gap to 4 mm to check the sparks strength. If it jumps the 4 mm gap, the sparks is adequate, if not, check the secondary side of the coil and the rpm signal.

900 The ECU and the fuel pump relay and the system relay are located on the right kick panel, under the dash. You must peel back the carpet to access them. This requires removing the sill plate and the carpet retaining strip at the a pillar. The relays are in holders above the ECU.

9000 The ECU is located under the left engine compartment plastic cover under the windshield. The main and pump relays are located in the fuse/relay panel behind the glove box. Remove the 6 screws in the front of the glove box and remove it, then drop the fuse panel down by removing the two screws securing it to the dash member. The panel is hinged at the rear, drop it down and out of its hinges to access the relays. The top of the glove box will be labeled for the relays there.

You need to unplug the ECU before making any checks on its wiring. Make sure the key is off before unplugging the ECU.

Quick Checks To Pinpoint

• Injector Signal While Cranking  Pull back the rubber boot to an injector connector. Measure across both wires there with a voltmeter while cranking the engine. Voltage will vary according to engine temperature, ranging from 1V when cold to 0.3V when at operating temperature. If the voltage is present across the injector, look back at the fuel flow/level and the spark, the ECU and its relays are working as they should. If not, continue on below.
• Power To Injectors  Again, at the wires to an injector, measure while cranking the engine except place the positive lead of your meter on the blue/red wire going to the injector and put the negative lead to a good ground. Now watch for battery voltage. If you have battery voltage, the relay circuits are working and you need to trace for a bad ECU, wiring. If the voltage still isn't there, continue on below.
• Power To 02 Sensor Preheater  Unplug the two wire connector to the oxygen sensor. Connect the voltmeter's positive lead to the blue/red wire after pulling back the harness side connector's boot. Attach the negative lead to a good ground. While cranking the engine look for battery voltage. If it is there, both relays and the ECU's pull down functions are working. Look for problems between ground side of injectors and ECU, or between terminal 87B of the fuel pump relay and the fuel pump. If no signal, check the fuse for the 02 preheater, an in line ceramic fuse on the right engine compartment fender well in a black holder, near the evaporator housing on 900s and under the windshield wipers on a 9000 or in the fuse box on both later cars. Check at the fuse for the voltage coming in and going out, sometimes the connector to the fuse gets pushed back or corroded. If the signal is not getting to the fuse, do the following test to check the systems relay. Also check the overboost switch operation on turbos

  Check that voltage is present on the overboost switch's pins 1 and 2 and that the wires are connected to its pins 1 and 2. If voltage goes in pin 1 but doesn't come out pin 2, the switch is faulty. For a temporary test, unplug the wires to the switch and jump them together. The switch is located under the left dash, has two wires and two vacuum hoses on it. Under no boost conditions, the switch should have continuity across its pins 1 and 2.

• Power To Air Mass Meter  With the key on and the ECU connected, check that pin 5 of the air mass meter has battery voltage. Disconnect the connector from the meter and pull back its boot and measure from the back of the connector. Attach the positive lead of the voltmeter to pin 5 and the negative lead to a good ground. If power is there, the system relay is ok. If not, proceed with the following ECU pin checks.

ECU PIN CHECKS

Check between ECU pin 35 and ground for battery voltage with the key on, ECU unplugged. If no voltage, check fuse 22 (900) and fuse 13 (9000).

Check between ECU pin 4 and ground for battery voltage. This is an unfused circuit. If there is no power, check the connections at the positive distribution panel. It is on the right fender well on a 900 and on the side of the battery box on a 9000. The small gauge positive wire from the positive battery terminal runs to it.

If voltage is present on pin 4, check the ECU grounds by checking across pin 4 and to pins 5 and 17. Attach the voltmeter's positive lead to pin 4 and the the negative leads to pins 5 and then 17. You should read battery voltage. If not, check the ground connections for these pins at the intake manifold near the engine lifting lug.

If the grounds are good, attach the positive lead of the voltmeter to pin 1 of the ECU connector and the negative lead to pin 17. Switch to an AC voltage scale and look for 2-3 V AC while cranking. If no signal, check the rpm signal circuits.

Jump pin 5 to pin 21. This should cause the system relay to close and provide power to pin 5 of the air mass meter. If not, go to the system relay checks below.

Jump pin 5 to pins 20 and 21. The pump relay and system relays should both close and the fuel pump should run. There should be power at the 02 sensor preheater and the injectors. If not, double check the turbo overboost switch and then troubleshoot the pump relay.

SYSTEM RELAY CHECKS

Pins 30 and 86 on the systems relay should be powered at all times. Measure their voltage by attaching the positive lead of the voltmeter to the pin and the negative lead to ground. Battery voltage should be present.

Pin 85 should have continuity to ECU pin 21. Measure with the ohm meter with both the relay and the ECU disconnected.

Jump pins 30 and 87B together. Battery voltage should then be present at pin 5 of the air mass meter and at the gray and white wire of the ELCD valve (charcoal canister).

Jump pins 30 and 87 together. There should be battery voltage at ECU pin 9, at the fuel pump relay pin 86 (through the turbo overboost switch if turbo).

FUEL PUMP RELAY CHECKS

Pin 30 of the fuel pump relay should be battery voltage all the time.

Check continuity with the ohm meter from pin 85 of the relay to pin 20 of the ECU, again, with both unplugged.

With the system relay in place and the key on, pin 86 of the pump relay should have battery voltage.

Jump pins 30 and 87B together, the fuel pump should run.

Jump pins 30 and 87 together, there should be voltage present at the 02 sensor's preheater circuit.

If all this checks good, reinstall the relays and while cranking the engine check for voltage at the blue/rd wires of the injectors while grounding ECU pins 5 and 17. Do this with the ECU unplugged. If the injectors and the fuel pump both run, and all other checks have been carried out and are good, the ECU is faulty.

If you replace the ECU, replace both the system and main relays at the same time. They have protection circuits in them to keep spikes off the ECU. It is these spikes that eats the ECUs. The added cost is little compared to the ECU. Also be very careful about the battery. Jump starting is a no-no unless unavoidable. Best thing to do is get another battery, or remove the battery from the car for charging. Spikes induced from jump starting or charging commonly take out the ECUs. Again, it might be less convenient, but it will be cheaper than toasting the ECU again.