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 .


PRELIMINARY CHECKS              WIRING DIAGRAMS

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.


Troubleshooting LH System No Start Causes

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


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.

 

 

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