C70 ECM electrical puzzler

RexxWonder · Post by **RexxWonder** » 29 May 2017, 15:35

Hello all,

I'm a new member and I've come here for help. A lifelong gearhead, I recently bought my daughter a 2002 C70 convertible with the 2.3T and Manual 5-speed. Only 74K miles, but obvious sun-damage, the can has run beautifully for almost a year.
A few weeks ago, I went to start it and check maintenance needs. While idling, the High-pressure a/c hose blew out of its crimp and a large cloud of coolant escaped. I just figured I would fix it later and went along with my inspection.
After I turned the engine off, I did a few things and tried to re-start it. The car just cranks with no spark. I tried a number of other options including checking all fuses and relay, but still no ignition...just the starter cranking.
The next morning I went out and it started on first crank, but as it warmed began to sputter and then died...and would not start again the rest of the day.
This pattern has repeated ever since. I plugged in the VIDA/DICE to see what happens:
-While running from first start, there are no codes at all
-Once it dies and will not re-start, it show the following codes:
-ECM-644A: Camshaft control - faulty position
-ECM-720A: Immobilizer communication - signal missing
-ECM-902A: Throttle unit communication - signal too low
-ECM-3200: Engine speed (RPM) sensor - signal missing

I have replaced the Cam sensor, RPM sensor, and Engine Coolant Temp sensor. Engine has good fuel pressure on crank, but after the first start, no spark.
The pattern of first-start/only-start never changes, but the order of the ERROR codes will change as well as add or subtract a few others indiscriminately.
I have to say that this issue has me thoroughly stumped. I would try and troubleshoot it electrically, but I really don't know where to start. I'm starting to think that there is a leaky capacitor somewhere (like in the ECM?) that will charge initially, but as it warms will begin to leak too quickly to support the attached controller. Because of the pattern, it would seem it has to be related to either temperature, or current flow (or both)...?
Also, could the a/c issue be at all related, or just a bizarre coincidence? I'd appreciate any pointers or help from the vast knowledge pool if you have other ideas.

Thanks in advance.

Post by **sleddriver** » 01 Jun 2017, 12:04

I saw this post below and remembered yours.

viewtopic.php?f=1&t=81067&start=30#p438380

Post by **abscate** » 01 Jun 2017, 15:06

I think that AC hose blowing has messed up your ETM wiring - that would explain the codes at least.

It is a real pig to look at on a turbo - you really have to take off the intake manifold to see it well. Maybe with a borescope or a mirror you can look at the harness?

Post by **precopster** » 01 Jun 2017, 15:12

That A/C pressure is enormous with the engine running. When that hose blew off it hit surrounding objects and damaged wiring.

There may be shorts with bare copper exposed. Disconnect the battery ASAP.

RexxWonder · Post by **RexxWonder** » 01 Jun 2017, 15:32

Thank you for the pointers. I was afraid of this possibility but still a little skeptical that the pattern of starting only on first crank was explained by what must be a very small break or gap in the wire insulation. I get it that the heat could cause the wires to expand and somehow widen such a gap, but why does it take all day and night to return to start mode?
I guess all it would take is one small crack and short to throw the signals off from everything...?

How does one go about finding such a short?

Post by **precopster** » 01 Jun 2017, 16:24

Find the impact point of the A/C hose. As previously suggested remove intake manifold. That will be the best bet

RexxWonder · Post by **RexxWonder** » 02 Jun 2017, 09:02

I know this sounds good and I'd love for it to be the solution, but looking at the position of the hose and crimp, the crimp faces down...so my logic tells me that the brunt of the force would have been on the ground.
I will check this possibility out, but are there any further suggestions? It seems the only way to prove this out will be to go to my local recycling yard and pull a harness from another C70 and replace the one in my car...not a trivial endeavor I'm sure.

Post by **abscate** » 03 Jun 2017, 06:13

If a high pressure AC hose let go, the hose will flail around in all directions like a high pressure fire hose, ripping holes in all kinds of things. I would get the manifold off to sort this out.

If it just blew the crimp and stayed intact, I agree it's probably another wiring fault somewhere else.

The start once , then no start scenario dies fit with immoboliser error on my 99. I have a u chipped key which will crank and start car once, then will crank only after that. I haven't tested to see how long it takes to reset.

Post by **mrbrian200** » 03 Jun 2017, 12:56

Also consider the PAG refrigerant oil would have misted the entire engine bay. As the car is older some weather pack seals around connectors may not be a perfect seal anymore. Light oils can also wick in between ground terminal rings and the chassis, as well as into wire terminal crimps and interfere with circuit continuity. You'll probably want to pick up a can of electrical contact cleaner. or two. Might want to unseat terminals from their connectors on affected circuits and solder the terminal crimps. Starts fine but loses continuity as things warm up is consistent with this sort of wire/electrical contact 'contamination'.

Post by **jimmy57** » 03 Jun 2017, 14:51

Un plug the a/c high pressure sensor from the line near the ECM box.
The high pressure sensor should have been informing the ECM of the pressure and turned on cooling fan and then turned fan to next higher speed. WHen the pressure continued to go higher ECM should turn off compressor. I'm thinking the high pressure sensor is kaput and the reference voltage is being drug down by the sensor and the other codes are from the signal values all being wonky as a result.