nostart2.2

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

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 three gallons of fuel are required to prime/fill the canister.
Check the fuses. All of them. Sometimes a fuse is critical to a system it is not labeled as protecting.

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.

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.

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

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.
Power To Air Mass Meter With the key on and the ECU connected, check that pin 2 of the air mass meter's connector has battery voltage. Unplug the connector from the air mass meter, pull back its boot and attach the positive lead of the voltmeter to pin 2 of the connector. Attach the negative lead to a good ground. If power is there, the system relay is good. If not, proceed with the following ECU pin checks.

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.

Back To Index