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Warm restart in limp mode - 2001 V70 T5

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volvolugnut
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Warm restart in limp mode - 2001 V70 T5

Post by volvolugnut » Mon Aug 12, 2019 2:15 pm

I have been trying to troubleshoot a problem with 2001 V70 with T5. About 6 times over 6 months time (about 2000 miles) I have had a problem when I start the engine. It immediately stumbles and idles rough. I can only keep running by giving partial throttle and will only rev to 1700 or 2500 RPM. If I can keep it running, I have crept home a few miles in this state. I believe it is in limp mode. A couple of times it 'cured itself' in about a mile. Every time it has restated fine after setting for a couple hours - even on 100 degree days.

Each time has been a restart after the engine is warmed. Never occurred at a cold start over night or setting for several hours. First 2 times were in 50 degree clear weather and last 4 times in 80 to 100 degrees.

This car has 197,000 miles and has seen mostly short trips on the last 50,000 miles in 8 years. It is in good mechanical condition and had XeModex electronic throttle replacement at 179,000 miles.

The last 3 times I have used Autophix scanner to read codes: CEM-DF13, ECM-902A, CEM-DF16, ECM-903F,CEM-1A5D AND ECM-4010. Best I can tell, these codes point to a short to power failure in the ETM wiring. The ECM-4010 is a long standing fuel tank vent issue that does not seem related to the other codes. There were a couple other codes that only occurred once: CEM-1A5F, CEM-1A61, CEM-1A62 and BCM-0065. I think these may be codes caused by the main 6 codes.

Since these problems started, I have recently cleaned the throttle plate - it was not very dirty. I replaced the battery - it was weak and old. I have cleaned the Plus power cable at the under hood cable end - not badly corroded. I have confirmed good voltage stopped and running at the front fuse box. Once, while in limp mode, I removed and replaced #7 fuse for ETM and did not hear the ETM buzz and then click in a few seconds.

I have been trying to get the problem to occur when sitting at home, but have not been able to get a failure to repeat in semi controlled conditions. I am currently removing wiring wrap on the fuse box to ETM to ECM to look for wire insulation failure.

I have read that 2004 models had a problem with overheating CEM under the dash. I suspect this might also be a problem on high mileage 2001 V70s in the southwest. This car has spent most of it's life in warm climate so has many thermal cycles on the CEM, ECM and TCM.
I have learned that the 2001 to 2003? V70s have air duct from the cabin to the ECM/TCM box under hood in front of right fender. When the AC in on cold and fan on high, there is a slight flow of cool air out the front of this box. One Volvo source called it the 'cool box'.

I have read several threads on this and other Volvo forums of similar random stalling problems in 2000-2005 Volvos. Most do not include a solution to the problem. A couple (2004 models) reported some success adding computer heat sinks to the CEM and adding fan to blow on the heat sinks.

Have others had similar resolved or unresolved problems with these models? Has time and miles created a new failure mode? Ideas?

volvolugnut



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Re: Warm restart in limp mode - 2001 V70 T5

Post by abscate » Tue Aug 13, 2019 3:58 am

The heat sink on CEM in hot climates is a known issue and worth exploring. I’ll try To find good threads


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volvolugnut
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Re: Warm restart in limp mode - 2001 V70 T5

Post by volvolugnut » Tue Aug 13, 2019 5:46 pm

Update:
I have also replaced the Engine Management (also called ETM) relay and cleaned the cabin air filter. Relay was replaced before the last failure.
Today I opened the wiring harness between ECM and the engine fuse box. Access is poor, but this can be done with air ducts and radiator fan removed. The wires along the bottom on the left side were very dirty, but I have not found any insulation damage yet. Still some portions to open harness and examine.
I have a tool for ECM and TCM removal to arrive in a couple days. I will then check the condition of contacts for the ECM and TCM in the enclosure box.



volvolugnut
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Re: Warm restart in limp mode - 2001 V70 T5

Post by volvolugnut » Sat Aug 24, 2019 3:05 pm

Status report on problem:
I have completed the wiring duct removal and opening of wiring between the fuse box and the ECM/TCM cool box on the passenger side of engine compartment. I opened the cool box, removed the ECM and TCM using the special tool. I inspected the wire connections on the bottom of these component connectors and checked for any corrosion. No problems found.

For general information, I have found the power wires from the front fuse box are routed in front of the radiator and do not travel in the wire duct just in front of the engine. Since this wire harness does not appear to have any CANbus wires, I have not inspected the wires in this duct across the front of the car.

I also cleaned and inspected the entire length of the green/white twisted pair CANbus which goes from the ECM to the ETM. I also inspected any wires I could identify as 12 volts from ECM and TCM that are included in the wire duct to the ETM. I did not find any breaks in the wires but did find some insulation that has been pinched. I will place electrical tape over each of these wires before bundling all the wires back in the ducts. I don't find evidence that these wires have shorted between CANbus and 12 volt, but want to assure it is not happening.

I also removed the CEM from the mounting bracket and inspected wires for any evidence of corrosion and chaffing. No problems found. I removed the climate controls and radio in center console. Inspected for corrosion and wire chaffing. No problems identified.
While the climate control is removed, I will replace bulbs.

While doing lots of restarts to try to get a repeat of the problem while parked at home, I reached the end of life for the ignition steering lock mechanism. I used the Dremel cutting disc to remove the broken parts so the key turns freely.

I have not identified any specific failure that may have caused the faults and start of limp mode as explained in my initial post. I have read other online information that points to Volvo software updates around 2005. These updates increase the delay time before a fault code is set for bad CANbus signals. Carfax report on this car does not show it has been to Volvo dealer since September 2004. What is everyone's thoughts on getting these later software updates?

Volvolugnut



volvolugnut
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Re: Warm restart in limp mode - 2001 V70 T5

Post by volvolugnut » Tue Sep 17, 2019 5:32 pm

Status report on this problem:
Short form - determined the CEM is failing due to heat. The CEM has been sent to be remanufactured by Xemodex.

More details on the problem: I hope this will be helpful to others. This is long and detailed and may read like a research report. I am very much the gray haired engineer.
I reassembled everything on the engine and wiring. I installed an inexpensive indoor/outdoor battery operated thermometer with the outdoor sensor taped to the CEM (Central Electronics Module) housing above the drivers left foot. I left the foot well covers removed. Then I drove around about 10 miles with several restarts. With the air conditioner and fan on, cabin temperature was in the low 70'sF. The CEM temperature climbed slowly to mid 90'sF. No problems with idling, driving or restarts. Ambient temperature was mid 80'sF.

I had been reading lots of internet information from various sources on CEM overheating. This appears to be a big problem noticed for 2004 and up Volvos, but was not noted as a problem for P2 Volvos. But, I was beginning to suspect my problem was related to overheating of the CEM. I read one report of testing with a hair dryer blowing on the CEM to see if it failed. A video at Xemodex showed a test with 90 C heat applied to the CEM during their performance test. Others have solved intermittent stalling, surging, limp mode and electrical failures by applying heat sinks and fans to the CEM electronic chips.

I decided to do a controlled test of heating the CEM. Since it is summer time and the car will get warm if left closed in the sun without air conditioner, I decided to let it idle and see if it would fail. I expected to try to restart after every interval of heating to see if it would fail to start. All previous failures had been away from home and I could not do much to troubleshoot before conditions changed. I have previously tried starting after sitting in the sun several hours and never reproduced the starting problem.

At the start of the test, the car was in full sun, facing west, ambient temperature about 95F, cabin temperature about 123F and CEM housing temperature about 118F. The engine had not been run more than a couple minutes in the last several hours. The indoor/outdoor thermometer was placed in the cup holder beside the radio in full sun. I started the car, left it idling in park with air conditioner and fan off and retreated to the cool house.

I was surprised with the test results! When I returned after 30 minutes, the engine had stalled and the thermometer display had blacked out. I had no way to know when the engine shut down or at what temperature. I moved the thermometer down to floor level and the display began to clear. After a minute or two with the door open the cabin temperature showed 115F and CEM housing 129F. The dash display showed outside temperature of 100F. Restart attempts failed, but the engine would crank.
I tried periodic starts for the next several hours without any success. I thought I may have fried the CEM or other parts. However, I had reproduced the failure to start problem and had some data.

The next morning with ambient temperature in the low 70's, I easily restarted the engine. I read fault codes and found they were mostly the same as other times when I had failure to restart when the weather and engine were hot. The only thing changing was temperature of the CEM. When the CEM was hot, the engine would not run.

I had been surprised how quickly CEM temperature increased during the first test. I erased all the codes and ran a new test to see if CEM temperature would increase after engine shut down. I ran the engine for 4 minutes and then shutdown. I left the door open to avoid any 'green house' heating effect. Cabin and CEM temperature were both 75F at the start of run time. The vehicle outdoor sensor read 93F (it was now in full sun and actual ambient was more like 85F). At engine shutdown, cabin and CEM were 77F. In 8 minutes the CEM temperature increased to 81F. Over the next hour cabin and CEM temperature both increased. For the first half hour the CEM was always about 3 degrees warmer and then CEM temperature matched then fell below cabin temperature. Maximum cabin temp was 86F and Maximum CEM temp was 85.2.
Conclusion: There is little continued heating of the CEM after the engine is shut down due to the CEM itself. However, cabin heat will slowly warm the CEM under the dash.

I decided to repeat the test with closer monitoring of time and temperatures. This time it was later in the afternoon and the windshield was in partial shade. Vehicle indicated temperature was 101F (likely actual 94F). Cabin temperature was 110F and CEM was 117F. Doors closed, air conditioner and fan off, engine started. 10 minutes later, engine stumbled and died. Cabin temperature 107, CEM temperature 118, outside vehicle indicated 100F. The engine would now crank but would not restart. With doors closed, at 8 minutes and also 14 minutes later, the cabin was 106F and the CEM was 120F.
Conclusion: When the CEM got to at least 120F it would fail and the engine would stop. Heat sinks and a cooling fan on the CEM might help, but these solutions might be marginal. I could envision a day where the car was heat soaked from running and parked with closed windows in the sun. Heat sinks and a fan would not be able to cool the CEM when inside temperature was over 120F from green house heating.

Next day I tried to restart the engine at 74F at the CEM housing. It would crank but not start. I checked the stored codes and got the normal codes I have been getting since this problem started.
Conclusion: The CEM is faulty and heat sinks and a fan would not help. I need a reliable vehicle that will start. I decided to remove the CEM and have Xemodex do the full remanufacture with cooling heat sinks (send in the core and $650). They will copy the program from the old CEM on the repaired CEM.

I sent the CEM out by UPS today. I will report on future developments.

volvolugnut



volvolugnut
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Re: Warm restart in limp mode - 2001 V70 T5

Post by volvolugnut » Sat Sep 28, 2019 6:01 pm

An update on my problem and what I have done to investigate the cause. Am I on track here or am I missing something I should be checking? What do you think of this problem and it's source?

The CEM has been tested by XeModex and found to be free of faults. They will charge $75 (plus shipping both ways) for the testing only without rebuild. Their techs suggest the problem may be the ETM or ECM and suggested I send them for testing. My ETM is a rebuilt unit from Xemodex replaced in 2016 so I think it is ok.

I continue to think it is a heat related problem occurring in the cabin. This points to the CEM (now declared ok) or any relays or wiring in the cabin. I have been testing any relays from the CEM assembly that are remotely related to the ETM or the ECM. The relays I selected to test are CMA2 X feed overload relay 2/30, CMA3 15 feed overload relay 2/31, CMI11 Fuel pump relay 2/23 and CMI22 Extended X feed relay 2/29 relays.

I have improvised a means to heat soak the relays with power supply and a bulb for loading. The test has been to hold for 5 to 10 minutes at 130 to 140 F. This temperature was selected because between 120 and 130 F inside my car the engine stumbled and stopped. The heat is supplied to the top of a metal coffee can by a heat gun cycled on and off to maintain the temperature. The relay and wires are hanging inside the can. An indoor/outdoor thermometer displays the temperature. Failure would be indicated if the loading bulb went off. So far, no relays have failed the test.

I have also started to check all relay and fuse terminals for loose terminal fit. I have found suitable thickness and width of metal to check the terminals for good friction. So far I have found a couple on the CEM board that were very loose and will adjust the grip mechanically by bending the terminal internals.

Am I on track here or am I missing something I should be checking? What do you think of this problem and it's source?

volvolugnut



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