NO START CHECKS 2.2 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 resistances, refer to a wiring diagram and insure you are measuring an isolated circuit, not one with parallel branches .
PRELIMINARY CHECKS            WIRING DIAGRAM

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 glovebox 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 glovebox. Remove the 6 screws in the front of the glovebox 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 glovebox 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 18 and ground for battery voltage with the key on, ECU unplugged. If no voltage, check fuse 22.

If voltage, check between pin 18 and pins 5, 11, and 25 with the key on, ECU unplugged. You should see battery voltage. This checks the grounds for the ECU. They are located at the intake manifold, near the lifting lug.

Check between pins 1 and 25 with the voltmeter on the ac volt scale. You should see 2-3 V AC while cranking the engine with the ECU unplugged. This is the rpm signal.

Jump pin 5 to pin 21 with ECU unplugged. Check for power to pin 2 of the air mass meter. If so, the system relay is closing as it should. If not, check the system relay as follows. Relay is labeled for its pins. Make sure you check the right pin on the holder as it will be a mirror image of the relay. The system relay is the one closest to the firewall, behind the fuel pump relay.

Relays pins 30 and 86 should have battery voltage at all times pin 85 of the relay should have continuity to ECU pin 21 (unplug relay to check at holder)

Jump 30 and 87B together and check for voltage at pin 2 of the air mass meter(brown/white wire) If no voltage, find wiring break.

Jump 30 and 87 together, check for voltage at the fuel pump relay pin 86 and ECU pin 9

Now go back to the ECU connector with it still unplugged. Jump pin 5 to 17 and 21. The fuel pump should run and you should have voltage on the blue/red wire to each injector and the 02 preheater. If not, check the fuel pump relay as follows. Use the same tips as for the system relay.

pin 30 battery voltage all the time

pin 85 check continuity to ECU pin 17

pin 86 should have voltage when system relay pins 30 and 87 are jumped or with system relay installed and key on

Jump 30 and 87B together. Fuel pump should run.

Jump 30 and 87 together. Injectors and 02 preheater should receive voltage.

If all this checks good, insure that the turbo overboost switch is functioning. Check that voltage is present on the 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.

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 17 and 21. 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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