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Old 04-09-2014, 04:53 PM   #1
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P1689 Control Unit Faulty

Has anyone seen a P1689 error code? My friend has a 97 Boxster with CEL, so we connected to my Durametric and here is what displayed:

P1126 O2 Sensor (4-6)
P1124 O2 Sensor (1-3)
P0102 Mass Air Flow Sensor Short Circuit/Open Circuit
P1689 Control Unit Faulty

The motor is running great with 60,000 miles on the clock. I did a search on this forum with this error code but not much found for this alarm.

Edit... I will add that the voltage on the pre-catalytic converter O2 sensors are flat on both banks (0 volts)

300K Mile Club

Last edited by Jager; 04-09-2014 at 04:58 PM.
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Old 04-10-2014, 08:47 AM   #2
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Jager, my Service manual says P1689 Engine control module faulty. If such faults occur, replace the ECM. No more info in the oem manual.
2000 S Speed Yellow LN 3.6L cylinders & pistons, triple row IMSB upgrade, R&R connecting rods, billet tensioner paddle&,oilpump driveshaft.Heads rebuilt by F6I with new valves & springs.Cayman airbox & MAF housing, 996 intake plenum & 75mm T/B. Fabspeedsport converters &Dansk muffler
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Old 04-10-2014, 02:59 PM   #3
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I guess I would start by seeing if there is voltage in the harness going to the O2 sensors. If not, it could be the ECU is dead. Is there a fuse or relay for the ECU? What do the voltage graphs look like for the sensors, before and after cats? The befores should look like a sine wave and the afters should be pretty close to a straight line.

Then, I would swap out the MAF with a known one to see if its good. There are also a couple of diagnostics for the MAF on the duramteric, voltage, I believe and maybe resistance.

Do the MAF values vary at all upon acceleration?
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1969(?) Fiat 850 Convertible
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1981 Alfa Romeo GTV 6
1985 Alfa Romeo Graduate
1985 Porsche 944
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Last edited by san rensho; 04-10-2014 at 03:01 PM.
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