It is late Thursday afternoon in mid-May and tourist season is just beginning in Colorado’s High Country. After finishing one mobile diagnosis, I was asked to look at another — a 2003 Honda Element with a no-cranking condition that had just been dropped off at my client shop’s busy parking lot by an owner who was now stranded 2,000 miles away from home.
The service notes attached to the repair order indicated that the owner replaced the battery in an attempt to fix the no-cranking condition, and that the owner’s hometown Honda dealer had previously replaced the instrument cluster to repair a blinking “Penny Arcade” warning light condition.
For that reason, my client shop asked if the Honda’s immobilizer system had, in some way, disabled the starter. An initial scan revealed diagnostic trouble codes (DTCs) P1298 (ELD circuit high voltage), P0600 (serial communication link malfunction) and ABS DTC #62-1 (ABS control unit, high IG2 voltage). See Photo 1.
After doing some basic research, none of the above DTC definitions appeared to be related to the no-cranking problem. Since my scan tool was communicating with the PCM and other modules, the P0600 appeared to be an intermittent DTC. Although the instrument panel check engine and immobilizer warning lights were blinking when we retrieved these DTCs, the lights disappeared once the new battery was recharged. See Photo 2.
I then attached an inductive amp probe to the battery negative cable so I could measure starter circuit draw. The Honda’s key-on, engine-off amperage draw was about 6 amps, while key-start amperage was about 13.8 amps. This would indicate that the fuel pump was adding about 5 amps and the pull-in solenoid was adding about 3 amps to the initial 6.0-amp key-on amperage draw. If the starter motor had engaged, amperage of at least 100 amps should have been added. I concluded that the starter likely needed to be replaced. See Photos 3 and 4.
In my experience, the reliability of Honda vehicles is such that I don’t get a lot of experience chasing multiple-code problems on body control electrical. Not only did I research my favorite database looking for blinking warning light problems, but I also prowled Internet DIY sites for case studies on the P0600 DTC. I found one for Honda with a P0600 DTC and blinking warning light problem, but it was a right-hand-drive model sold in England.
While Honda’s electrical architecture is relatively simple, it isn’t typical because it uses two “main relays” to control many electrical/electronic functions. As they pertain to the above DTCs, B+ voltage to PGM-F1 Main Relay One is supplied by underhood fuse #6, 15 amps. The PCM activates Main Relay One by grounding its control circuit at PCM pin #E7. When Main Relay One is activated, B+ is supplied to PCM power input pins A1 and A2. Main Relay One also supplies control current to Main Relay Two, which activates the fuel pump when PCM pin #E17 grounds Relay Two’s control circuit. The PCM itself is grounded to G101, which is located at the front of the cylinder head.
The immobilizer B+ is supplied by underhood fuse #9, 10 amps. B+ passes through the underdash fuse relay box and exits to pin #7 on the “immobilizer control unit-receiver.” The immobilizer control unit-receiver connects to PCM pin #E3 (logic ground) and also connects through a “multiplex control unit” to PCM pin #E27 (immobilizer input). The parking brake switch also provides an input to the immobilizer unit.
The Honda’s starter was replaced Friday afternoon and the engine started and ran normally. Case closed? Not really, because the problem with the new Honda instrument cluster lighting up like a penny arcade and the discharged condition of the new battery continued to haunt me.
According to my service information, the immobilizer should disable the fuel system if it can’t recognize the ignition key. According to my stored scan data, the Honda’s immobilizer was in the “RUN” mode, so the immobilizer was indeed recognizing the ignition key. If the immobilizer had failed to identify the ignition key, scan data would have indicated the “BAN” or fuel-disable mode.
The P1298 Electrical Load Detector (ELD) high-voltage problem is even more puzzling. Enable criteria include, DTC P1297 not present, system voltage more than 10.0 volts (headlights on) and the PCM detecting more than 4.95 volts on the ELD signal circuit for at least five seconds. The ELD reports to the PCM the amount of current flowing through the ignition switch. If the ELD signal voltage is too high, DTC P1298 will be set. The P0600 DTC was more problematic because it indicated that the PCM, the Honda’s Multiplex Control Unit and the gauge assembly might not be communicating.
The P0600 enable conditions are simply that the ignition switch is turned on and that the interruption in communications occurs for more than five seconds. A note also indicates that P0600 is stored “when there is a problem in the body electrical system.” Pretty fuzzy explanation, but we’re working in the real world that, in this case, was the parking lot of a local undercar shop armed with a schematic in one hand and a voltmeter in the other.
To complicate the issue, discovering failure patterns can be difficult, especially when the condition occurs intermittently and behaves erratically. To summarize my findings, the slow cranking speed of the engine indicated that the battery’s state-of-charge (SOC) was very low. I also measured about a 0.500-amp drain on the battery-to-engine ground cable and about 0.500 amps on the battery-to-chassis ground, both of which amounted to a one-amp drain, which was sufficient to discharge the battery over the weekend. See Photo 5.
Turning on the key, the orange “check engine” (CE) light and the green-key immobilizer warning light were now blinking, along with a muted clicking noise emanating from the center-right of the dash, which I assumed was Main Relay One or Two.
More noteworthy, the instrument gauges were operating intermittently after startup. Sometimes a key-on/key-off cycle would restore gauge operation. Disconnecting and reconnecting the battery would temporarily restore the instrument panel operation. Last, but not least, a 500 mA Ac voltage spike occasionally registered on my digital voltmeter. Could the Honda’s alternator have a loose diode? Possibly so.
DTCS & SCHEMATICS
The Honda would start and run, so its owner wanted to return to his hometown Honda dealership to have the newly installed instrument cluster/gauge replaced under warranty. Not content to let the matter go, the Honda Element’s problem still mystified me.
The immobilizer wiring schematic offered a good place to begin establishing the relationship between the P1298 (ELD circuit high voltage), P0600 (serial communication link malfunction) and ABS DTC #62-1 (ABS control unit – high IG2 voltage) trouble codes and the penny arcade symptoms displayed by our Honda Element’s instrument panel. The previously erased ABS high-voltage DTC #62-1 didn’t return, so I began looking for a common cause of the P1298 and P0600 DTCs.
Looking at the immobilizer schematic, the white PCM “E” connector contained the battery voltage input (pin #E9), PGM-F1 relay control (pin #E7), the immobilizer logic ground (pin #E3), immobilizer input (pin #E27) and the malfunction indicator light (MIL) (pin #E31), all of which are related to this Honda’s DTCs.
The PCM grounds through pins LG1 and LG2, which ground through G101 located on the front of the engine. Keep in mind that G101 ultimately grounds to the battery negative through ground T3 located on the automatic transmission. A loose ground connection at T3 might cause the orange check engine and green key immobilizer lights to flicker.
A loose ground connection might also cause Main Relay One to chatter and it might also cause a slow cranking condition, even when the battery is fully charged. While we might ultimately be looking at a bad PCM, a thorough inspection of grounds G101 and T3 and PCM connector “E” would be a good place to begin this month’s Diagnostic Solution.
Other than disconnecting/connecting the alternator and recharging the battery, the greatest amount of time spent doing this diagnosis was in downloading and analyzing approximately 15 pages of schematics and service information.
As even “grocery-getter” imports become more complex, a greater learning curve will be required to diagnose multiple DTCs and system issues like those described above. In-depth diagnostics cost time and money and often involve a long and complex learning curve, all of which are issues that our industry in general should understand.