Volvo RWD 900 Forum

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Bought this car from an older couple about a year ago. It starts every morning when engine is cold and ran perfectly under normal weather in San Francisco (55 -75F). But when the weather is hot (80-90F), and the car has been driven for about 30 minutes ( engine hot), it will not start again after the engine is turned off. The starter will not crank when the key is turned to the start position. You only hear a click. This happen only intermittently. Sometines the car will start again after waiting for 15-30 minutes without doing anything. And sometines it will start immediately with the help of battery booster. I have check or replaced the following items:
1) Battery -replaced
2) Positive and Negative battery cables - replaced
3) Stater - replaced
4) Starter switch - replaced
5) Alternator - check,charging at 14.2V
6) Safety Neutral Switch - check, step on brake, key in position 2, drive selector moves through the drive positions.

Anyone came across this problem before ? Could this be caused by infamous Bosch wiring harness ? ECU ? Thanks, Andrew

Another and more probable fault is in the PNP switch, a combination neutral safety switch and gear selected sensor and reverse light switch.

Bet your reverse lights are not functioning. The FAQ has replacement directions, but the switch itself can be repaired, all that has happened is because of the switch proximity to the exhaust down pipe has caused the grease to dry out and harden, making the internal electrical contacts not function, take it apart and re grease with a good synthetic and re position. Mark the placement of the bolt thru the switch, the bolt hole is slotted for adjustment.

Another way to tell, is when it will not start, is to turn the key on to run, place foot on brake pedal and row the gear selector back and forth thru the whole range of gears, do this about 30 times. The try starting.

It very well could be an electrical issue as the other post suggests, but odds are it is the PNP switch, that is where I would start.

DanR '94 964 343,000 miles (109,000 on the new engine)
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DanR

Hello Dan: The PNP was the amount the first things I checked out. The test procedures I did were 1) Foot on brake pedal, key in position # 2, then moved the drive mode selector through the varies postions. I was able to do this test without any problem. 2) The reverse light comes on when I select the reverse mode each time. 3) The PNP was removed, the black grease and contacts inside were cleaned, then repacked with new electrical grease. After doing these tests, I am quite certain the PNP is not my problem. Many thanks, Andrew

Howdy Andrew,

Heat soak related faults are almost always resistive contacts. Having said that, it doesn't mean that is your problem, only something I keep in mind when approaching a heat related problem.

Next time it fails to start, clamp one of your booster cables to the body of the starter and the other end of the same cable to the negative terminal of the battery. If the starter turns, look for a defective ground between the starter and engine or engine and chassis. If it does not, you have eliminated that as a possibility.

Notice in the simplified drawing that you can bypass the interlocks at the service wire (pink wire; should be near the firewall, I think). Jumper it to the blue/pink wire on the same connector. If the starter turns with the key in the START position, you've got it narrowed to an interlock problem. (BTW, disconnect that connector and inspect the pins and wires for corrosion while you are there.)

If jumping around the interlock doesn't do it, you will need to start measuring and recording voltages at various points before, during, and after failure mode. The most meaningful first checks will be directly on the starter connections. Then you will know whether the problem is on the 50 line or the 30 line. You may find it advantageous to connect a voltmeter semi-permanently to the starter service connector (50 line) so you can see it from the cockpit.




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Mr. Shannon DeWolfe -- I've taken to using mister because my name misleads folks on the WWW. I am a 53 year old fat man. ;-)

Hello Shannon: Following your suggestion, I traced the Blu/Pink wire to the harness connector that is connected to the NPN on the left hand side of the trans. The insulation of that wire was pinched in two small areas, 1/2" above the terminal. Some of the copper wires were in the open. Maybe during hot days, the heat generated by the trans and the weather, is high enough to cause this wire to heat up and increase its resistance, therefore the no crank condition. Andrew

Hello Shannon: Much thanks for your suggestions. Since my electrical knowledge is limited, please help me with the following questions:

1) On your suggestion #2, is the "Interlocks" the same as the "PNP Switch" ? You also said " BTW, disconnect that connector.....", what is BWW ? What connector ? Where is this connector ?

2) How should I look for the interlocks service connector near the firewall? Is it square, open or with cover,and how many wires ?

3) What are the normal readings at the 30(red), 50(blu/pnk) starter terminals at different points of the stating process ?

Many thanks, Andrew

BTW= By The Way